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

Summary

Google::Protobuf::ListValue includes Enumerable, but its handwritten each unconditionally yields. Calling each without a block raises LocalJumpError instead of returning an Enumerator, unlike the Array-like Ruby contract.

Proposed correction

Return enum_for(:each) when no block is provided. Candidate: 0092fd7f345b6c970e72895423487d01f11abab6.

The isolated model fails on current main (5b1c20741838b8359193b97895cb0ff35b4ecf79) and passes the candidate with chained enumeration and converted Ruby values. 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 at the handwritten Google::Protobuf::ListValue#each entry point and reproduce the no-block call described in the issue. Verify that no-block and chained enumeration return converted Ruby values, then run the native and FFI suites noted in the report; done means both behaviors work without regressions.