[ECO-5465] Port remaining high-value JS integration tests

[lawrence-forooghian]

Note: This PR is based on top of #63; please review that one first.

This ports the remaining high-value JS integration tests, continuing the work started in fa255c1. I've created #60 for mopping up the remaining work, but I think that these tests should give us enough confidence for our v0 release. See commit messages for more details.

Summary by CodeRabbit

• New Features

  • Configurable garbage-collection settings for realtime objects via client options (defaults preserved).

• Tests

  • Test-only hook to override outbound publish behavior.
  • Test-facing GC completion stream to observe garbage-collection cycles.
  • Improved test helpers and subscriber listener APIs.
  • Migrated JS integration tests to a new wire-format.

• Documentation

  • Fixed a typo in JSON serialization docs.

• Chores

  • Updated a dependency submodule to a newer commit.