Unable to build certificate with P384 from version 0.3.0

A number of type/trait changes have occured with 0.3.0. Notably, this has broken certificate building with ECDSA P384 Signing keys.

Consider:

let int_cert = builder
        .build::<_, DerSignature>(&root_signing_key)
        .expect("failed to build intermediate CA certificate");

Where root_signing_key is of the type SigningKey<NistP384>

This yields the following errors:

error[E0277]: the trait bound `&ecdsa::SigningKey<NistP384>: ecdsa::signature::Signer<ecdsa::der::Signature<NistP384>>` is not satisfied
   --> src/test_ca.rs:307:18
    |
307 |         .build::<_, DerSignature>(&root_signing_key)
    |          -----   ^ the trait `ecdsa::signature::Signer<ecdsa::der::Signature<NistP384>>` is not implemented for `&ecdsa::SigningKey<NistP384>`
    |          |
    |          required by a bound introduced by this call
    |
help: `ecdsa::SigningKey<C>` implements trait `ecdsa::signature::Signer<S>`
   --> /Users/william/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/ecdsa-0.17.0/src/signing.rs:180:1
    |
180 | / impl<C> Signer<Signature<C>> for SigningKey<C>
181 | | where
182 | |     C: EcdsaCurve + CurveArithmetic + DigestAlgorithm,
183 | |     Scalar<C>: Invert<Output = CtOption<Scalar<C>>>,
    | |____________________________________________________^ `ecdsa::signature::Signer<ecdsa::Signature<C>>`
...
282 | / impl<C> Signer<SignatureWithOid<C>> for SigningKey<C>
283 | | where
284 | |     C: EcdsaCurve + CurveArithmetic + DigestAlgorithm,
285 | |     C::Digest: AssociatedOid,
286 | |     Scalar<C>: Invert<Output = CtOption<Scalar<C>>>,
    | |____________________________________________________^ `ecdsa::signature::Signer<SignatureWithOid<C>>`
...
321 | / impl<C> Signer<der::Signature<C>> for SigningKey<C>
322 | | where
323 | |     C: EcdsaCurve + CurveArithmetic + DigestAlgorithm,
324 | |     Scalar<C>: Invert<Output = CtOption<Scalar<C>>>,
325 | |     der::MaxSize<C>: ArraySize,
326 | |     <FieldBytesSize<C> as Add>::Output: Add<der::MaxOverhead> + ArraySize,
    | |__________________________________________________________________________^ `ecdsa::signature::Signer<ecdsa::der::Signature<C>>`
    |
   ::: /Users/william/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/ecdsa-0.17.0/src/recovery.rs:283:1
    |
283 | / impl<C> Signer<(Signature<C>, RecoveryId)> for SigningKey<C>
284 | | where
285 | |     C: EcdsaCurve + CurveArithmetic + DigestAlgorithm,
286 | |     Scalar<C>: Invert<Output = CtOption<Scalar<C>>>,
    | |____________________________________________________^ `ecdsa::signature::Signer<(ecdsa::Signature<C>, RecoveryId)>`
note: required by a bound in `build`
   --> /Users/william/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/x509-cert-0.3.0/src/builder.rs:291:12
    |
289 |     fn build<S, Signature>(mut self, signer: &S) -> Result<Self::Output>
    |        ----- required by a bound in this associated function
290 |     where
291 |         S: Signer<Signature>,
    |            ^^^^^^^^^^^^^^^^^ required by this bound in `Builder::build`

error[E0277]: the trait bound `&ecdsa::SigningKey<NistP384>: Keypair` is not satisfied
   --> src/test_ca.rs:307:18
    |
307 |         .build::<_, DerSignature>(&root_signing_key)
    |          -----   ^ the trait `KeypairRef` is not implemented for `&ecdsa::SigningKey<NistP384>`
    |          |
    |          required by a bound introduced by this call
    |
help: the trait `KeypairRef` is implemented for `ecdsa::SigningKey<C>`
   --> /Users/william/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/ecdsa-0.17.0/src/signing.rs:568:1
    |
568 | / impl<C> KeypairRef for SigningKey<C>
569 | | where
570 | |     C: EcdsaCurve + CurveArithmetic,
571 | |     Scalar<C>: Invert<Output = CtOption<Scalar<C>>>,
    | |____________________________________________________^
    = note: required for `&ecdsa::SigningKey<NistP384>` to implement `Keypair`
note: required by a bound in `build`
   --> /Users/william/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/x509-cert-0.3.0/src/builder.rs:292:12
    |
289 |     fn build<S, Signature>(mut self, signer: &S) -> Result<Self::Output>
    |        ----- required by a bound in this associated function
...
292 |         S: Keypair + DynSignatureAlgorithmIdentifier,
    |            ^^^^^^^ required by this bound in `Builder::build`

error[E0277]: the trait bound `&ecdsa::SigningKey<NistP384>: DynSignatureAlgorithmIdentifier` is not satisfied
   --> src/test_ca.rs:307:18
    |
307 |         .build::<_, DerSignature>(&root_signing_key)
    |          -----   ^ the trait `SignatureAlgorithmIdentifier` is not implemented for `&ecdsa::SigningKey<NistP384>`
    |          |
    |          required by a bound introduced by this call
    |
help: the trait `SignatureAlgorithmIdentifier` is implemented for `ecdsa::SigningKey<C>`

The causes P385 certificate signers to fail to compile. Given the complexity of the types and traits involved I haven't been able to resolve this for a few hours :(

My assumption is that there are either missing traits or something silly that is being missed here.

Start with the failing call in src/test_ca.rs:307 and compare it with the build bounds shown in x509-cert-0.3.0/src/builder.rs. Trace the P384 SigningKey trait implementations referenced in the compiler output, then verify that building a certificate with this signer compiles and succeeds.