abi.decode failing with "Stack too deep" for a list of structs when optimizations are enabled

## Description

Abi decoding `SomeStruct[]` fails with

```
CompilerError: Stack too deep. Try compiling with `--via-ir` (cli) or the equivalent `viaIR: true` (standard JSON) while enabling the optimizer. Otherwise, try removing local variables. When compiling inline assembly: Variable headStart is 3 slot(s) too deep inside the stack.K
```

Strangely, wrapping it in a struct with a `SomeStruct` field on it "fixes" the issue

https://github.com/beehive-innovation/rain-protocol/pull/452/files#diff-e5cf60434f03c13e62d93df0932957c2208a64a15065489486b9aea0d158e723R9

```
SomeStruct[] memory foo_ = abi.decode(data_, (SomeStruct[]));
```

fails, as does

```
struct Foo {
SomeStruct[] bar;
}
```

but this passes

```
struct Foo {
SomeStruct bar;
SomeStruct[] baz;
}
```

The issue only appears with compiler optimizations enabled and appears for both IR and non-IR

## Environment

- Compiler version: 0.8.17
- Target EVM version (as per compiler settings):
- Framework/IDE (e.g. Truffle or Remix): hardhat
- EVM execution environment / backend / blockchain client:
- Operating system:

## Steps to Reproduce

https://github.com/beehive-innovation/rain-protocol/pull/452/files#diff-e5cf60434f03c13e62d93df0932957c2208a64a15065489486b9aea0d158e723R9

Reproduce the linked PR #452 example with Solidity 0.8.17 in Hardhat, with optimizations enabled, comparing direct SomeStruct[] decoding with the two wrapper-struct forms. Done means the direct array decode no longer produces Stack too deep for both IR and non-IR compilation.

Written by the indexing model from the issue text.