Finish porting of JS integration tests

[lawrence-forooghian]

• check through the code the LLM generated
• for correctness
• for consistency
• implement the remaining test cases (TODO link to my plan)
• bring in line with latest ably-js
• write whatever documentation would be useful for porting further test cases in the future (see prompts on branch integration-test-porting-prompts)

┆Issue is synchronized with this Jira Task by Unito