fix: allow relay to forward unlimited bytes

[drHuangMHT]

Description

Allow relay to forward unlimited bytes from one peer to another by checking if max_circuit_bytes equals to 0 before checking if bytes_sent exceeds max_circuit_bytes.
This will make current implementation follow the spec.
May close #5170.

Notes & open questions

Not sure how to write the test.

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

[drHuangMHT]

Changelog entry will be added if the fix is accepted, discussion welcome.

[jxs]

thanks @drHuangMHT! LGTM just one nitpick. Can you also add a CHANGELOG.md entry and Cargo.toml update please?
cc @dariusc93

[jxs]

ah sorry, it's still missing the Cargo.toml version bump

[drHuangMHT]

@jxs Need send-it lable and probably a re-approval to merge this