[Ruby] RepeatedField#each raises without a block instead of returning an Enumerator

Summary

Both native and FFI Google::Protobuf::RepeatedField#each require a block and raise LocalJumpError when called blocklessly, despite RepeatedField including Enumerable and presenting an Array-like API.

Proposed correction

Wrap the implementation-specific each so a missing block returns enum_for(:each) and block calls continue to use the native/FFI implementation. Candidate: 69cf8afde5a36d46c31aac7270cf8886b714ab25 on current main (5b1c20741838b8359193b97895cb0ff35b4ecf79).

The isolated model covers native and source-built FFI enumeration. The cumulative candidate passes 332 native tests /556,948 assertions and 329 FFI tests /598,403 assertions with no failures or errors (documented omissions only).

I used an AI coding assistant during source review and verification. I am opening an issue first because CONTRIBUTING asks for tests and maintainer agreement; this dependency audit is not permitted to modify repository tests and no CLA was signed as part of it.

Start by comparing the native and FFI implementations of Google::Protobuf::RepeatedField#each on current main with candidate 69cf8afde5a36d46c31aac7270cf8886b714ab25. Verify blockless calls return an Enumerator while block calls preserve existing behavior, then run the native and source-built FFI enumeration tests described in the issue and confirm there are no failures or errors.