TidalAPI: accept flexible create dry-run responses

[stefanmoro]

Summary

• accept resource-create dry runs that succeed with no representation, whether the server responds with the current empty 204 or another successful 2xx
• treat a generic JSON:API success document as an absent typed create body while keeping ordinary typed create decoding strict
• add regression coverage for current/future empty and generic responses, normal typed creates, and malformed typed responses

Context

Server PR #1787 keeps resource-create dryRun at 204 with no body while standardizing normal creates to 201 and non-create mutations to 200. A later server change may make create dryRun an ordinary successful 2xx, with an empty body or a minimal JSON:API document.

Retrofit already accepts all successful 2xx responses and handles 204. This closes the 200/202 response-conversion gap without weakening typed create responses.

There are currently no first-party Android call sites for artistsPost or appreciationsPost, but the shared SDK boundary needs to be forward-compatible before one is added.

Verification

• changed-file ktfmt lint
• ./gradlew :tidalapi:testDebugUnitTest :tidalapi:lint