fix: handle bytes in map and repeated fields in toProto3JSON

[mjameswh]

Summary

• toProto3JSON failed to base64-encode bytes values inside map and repeated fields
• Moved Buffer/Uint8Array handling into convertSingleValue so it applies everywhere, not just top-level fields

Fixes #7704

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[gemini-code-assist]

Code Review

This pull request adds support for bytes fields within maps and repeated fields in the proto3-json-serializer-nodejs package. It updates the proto definitions, test fixtures, and the serialization logic in toproto3json.ts by moving the byte conversion logic into convertSingleValue. New unit tests for map and repeated byte fields are also included. I have no feedback to provide.

[mjameswh]

For info, I believe our company has already signed the CLA; I'm working internally on getting added to the authorized list of emails.