feat(request-response): configurable use of relayed connections

[MatthiasvB]

Description

Add a config flag controlling whether outbound requests may be sent over relay connections. Defaults to enabled (current behaviour); when disabled, only direct connections are used, conserving relay bandwidth. Also filter relayed addresses via multiaddr::Protocol and tolerate the extended DialFailure fields.

Fixes #6238.

AI Assistance Disclosure

Tools used Github Copilot, Claude Code

Attestation (required):

• I have read every line of this diff, understand what it does, and can explain it in review.

Change checklist

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• A changelog entry has been made in the appropriate crates

[dariusc93]

This sounds more like a user-specific use-case, in which case wouldnt it make more sense to write a behaviour, wrapping around request-response to perform the filtering based on a specified configuration?

[MatthiasvB]

This sounds more like a user-specific use-case, in which case wouldnt it make more sense to write a behaviour, wrapping around request-response to perform the filtering based on a specified configuration?

Interesting idea. I'm not deeply familiar with the rust-libp2p internals, so the feasibility of this I can't judge. My instinct would tell me that a wrapper around request-response would have a hard time modifying its internal behaviour. Could you give me a few pointers on the architectural decisions that might enable such a wrapper?