Implement Retrieval Timeout

[lidel]

Service Worker should have a configurable Retrieval Timeout, set to 30s by default to match current UX of Kubo, Rainbow, ipfs.io / dweb.link:

Gateway.RetrievalTimeout at kubo/docs/config.md:

Timeout behavior:

• Time to first byte: Returns 504 Gateway Timeout if the gateway cannot start writing within this duration (e.g., stuck searching for providers)
• Time between writes: After first byte [block], timeout resets with each write [block]. Response terminates if no new data [block] can be written within this duration

Prior art GO code:

• feat(config): Gateway.RetrievalTimeout|MaxConcurrentRequests kubo#10905
  • feat(gateway): concurrency and timeout limits boxo#994

[achingbrain]

This is already partially implemented though it doesn't reset between blocks.

We probably don't need to go to the level of blocks specifically, we can just wrap the @helia/verified-fetch response body stream and reset a timer every time any chunk of data is sent to the caller.