GHC 9.6.3 support

Hello,
I've just tried compiling servant-multipart with GHC 9.6.3 and am hitting this issue:

```
servant-multipart-client> build
servant-multipart-client> Preprocessing executable 'server' for servant-multipart-client-0.12.1..
servant-multipart-client> Building executable 'server' for servant-multipart-client-0.12.1..
servant-multipart-client> [1 of 1] Compiling Main
servant-multipart-client> [2 of 2] Linking .stack-work/dist/aarch64-osx/Cabal-3.10.1.0/build/server/server
servant-multipart-client> ld: warning: ignoring duplicate libraries: '-lm'
servant-multipart-client> Preprocessing library for servant-multipart-client-0.12.1..
servant-multipart-client> Building library for servant-multipart-client-0.12.1..
servant-multipart-client> [1 of 1] Compiling Servant.Multipart.Client
servant-multipart-client>
servant-multipart-client> /private/var/folders/0c/zmpjp7l568xcvnt49pkkn5p00000gn/T/stack-29e507a3bc44f1b9/servant-multipart-client-0.12.1/src/Servant/Multipart/Client.hs:77:18: error: [GHC-39999]
servant-multipart-client> • Ambiguous type variable ‘f1’ arising from a use of ‘source’
servant-multipart-client> prevents the constraint ‘(Foldable f1)’ from being solved.
servant-multipart-client> Probable fix: use a type annotation to specify what ‘f1’ should be.
servant-multipart-client> Potentially matching instances:
servant-multipart-client> instance Foldable (Either a) -- Defined in ‘Data.Foldable’
servant-multipart-client> instance Foldable Proxy -- Defined in ‘Data.Foldable’
servant-multipart-client> ...plus 7 others
servant-multipart-client> ...plus 93 instances involving out-of-scope types
servant-multipart-client> (use -fprint-potential-instances to see them all)
servant-multipart-client> • In the first argument of ‘(.)’, namely ‘source’
servant-multipart-client> In the expression: source . pure
servant-multipart-client> In an equation for ‘loadFile’: loadFile _ = source . pure
servant-multipart-client> |
servant-multipart-client> 77 | loadFile _ = source . pure
servant-multipart-client> | ^^^^^^
servant-multipart-client>
servant-multipart-client> /private/var/folders/0c/zmpjp7l568xcvnt49pkkn5p00000gn/T/stack-29e507a3bc44f1b9/servant-multipart-client-0.12.1/src/Servant/Multipart/Client.hs:77:27: error: [GHC-39999]
servant-multipart-client> • Ambiguous type variable ‘f1’ arising from a use of ‘pure’
servant-multipart-client> prevents the constraint ‘(Applicative f1)’ from being solved.
servant-multipart-client> Probable fix: use a type annotation to specify what ‘f1’ should be.
servant-multipart-client> Potentially matching instances:
servant-multipart-client> instance Applicative (Either e) -- Defined in ‘Data.Either’
servant-multipart-client> instance Applicative Proxy -- Defined in ‘Data.Proxy’
servant-multipart-client> ...plus 8 others
servant-multipart-client> ...plus 75 instances involving out-of-scope types
servant-multipart-client> (use -fprint-potential-instances to see them all)
servant-multipart-client> • In the second argument of ‘(.)’, namely ‘pure’
servant-multipart-client> In the expression: source . pure
servant-multipart-client> In an equation for ‘loadFile’: loadFile _ = source . pure
servant-multipart-client> |
servant-multipart-client> 77 | loadFile _ = source . pure
servant-multipart-client> | ^^^^
servant-multipart-client>
servant-multipart-client> /private/var/folders/0c/zmpjp7l568xcvnt49pkkn5p00000gn/T/stack-29e507a3bc44f1b9/servant-multipart-client-0.12.1/src/Servant/Multipart/Client.hs:135:37: error: [GHC-39999]
servant-multipart-client> • Could not deduce ‘Foldable f0’ arising from a use of ‘source’
servant-multipart-client> from the context: MultipartClient tag
servant-multipart-client> bound by the type signature for:
servant-multipart-client> multipartToBody :: forall tag.
servant-multipart-client> MultipartClient tag =>
servant-multipart-client> LBS.ByteString -> MultipartData tag -> RequestBody
servant-multipart-client> at src/Servant/Multipart/Client.hs:(111,1)-(115,30)
servant-multipart-client> The type variable ‘f0’ is ambiguous
servant-multipart-client> Potentially matching instances:
servant-multipart-client> instance Foldable (Either a) -- Defined in ‘Data.Foldable’
servant-multipart-client> instance Foldable Proxy -- Defined in ‘Data.Foldable’
servant-multipart-client> ...plus 7 others
servant-multipart-client> ...plus 93 instances involving out-of-scope types
servant-multipart-client> (use -fprint-potential-instances to see them all)
servant-multipart-client> • In the first argument of ‘(.)’, namely ‘source’
servant-multipart-client> In the first argument of ‘($)’, namely
servant-multipart-client> ‘source . pure . lencode . iValue’
servant-multipart-client> In the fourth argument of ‘renderPart’, namely
servant-multipart-client> ‘(source . pure . lencode . iValue $ input)’
servant-multipart-client> |
servant-multipart-client> 135 | (source . pure . lencode . iValue $ input)
servant-multipart-client> | ^^^^^^
servant-multipart-client>
servant-multipart-client> /private/var/folders/0c/zmpjp7l568xcvnt49pkkn5p00000gn/T/stack-29e507a3bc44f1b9/servant-multipart-client-0.12.1/src/Servant/Multipart/Client.hs:135:46: error: [GHC-39999]
servant-multipart-client> • Could not deduce ‘Applicative f0’ arising from a use of ‘pure’
servant-multipart-client> from the context: MultipartClient tag
servant-multipart-client> bound by the type signature for:
servant-multipart-client> multipartToBody :: forall tag.
servant-multipart-client> MultipartClient tag =>
servant-multipart-client> LBS.ByteString -> MultipartData tag -> RequestBody
servant-multipart-client> at src/Servant/Multipart/Client.hs:(111,1)-(115,30)
servant-multipart-client> The type variable ‘f0’ is ambiguous
servant-multipart-client> Potentially matching instances:
servant-multipart-client> instance Applicative (Either e) -- Defined in ‘Data.Either’
servant-multipart-client> instance Applicative Proxy -- Defined in ‘Data.Proxy’
servant-multipart-client> ...plus 8 others
servant-multipart-client> ...plus 75 instances involving out-of-scope types
servant-multipart-client> (use -fprint-potential-instances to see them all)
servant-multipart-client> • In the first argument of ‘(.)’, namely ‘pure’
servant-multipart-client> In the second argument of ‘(.)’, namely ‘pure . lencode . iValue’
servant-multipart-client> In the first argument of ‘($)’, namely
servant-multipart-client> ‘source . pure . lencode . iValue’
servant-multipart-client> |
servant-multipart-client> 135 | (source . pure . lencode . iValue $ input)
servant-multipart-client> | ^^^^
```

Start with src/Servant/Multipart/Client.hs, especially the loadFile definition at line 77 and multipartToBody around line 135. Reproduce the failure by building servant-multipart-client with GHC 9.6.3, then verify that the package builds successfully without the reported ambiguous Foldable and Applicative errors.

Written by the indexing model from the issue text.