### Changes:
- `HTTPClient` has a new `X-Post-Params-Hash` request header
- Replaced `HTTPRequest.Method.post`'s `Encodable` value with a more
specific `HTTPRequestBody` (like `HTTPResponseBody`)
- `HTTPRequestBody` allows overriding `contentForSignature` (it defaults
to `[]`) which then `Signing` uses for the hash
- Fixed `LogInOperation` not passing the `VerificationResult` to the
result `CustomerInfo`. This is captured in unit and integration tests
now.
- Add support for signing `POST` requests in `Path.logIn` and
`Path.postReceiptData`
Depends on https://github.com/RevenueCat/khepri/pull/6246
