Title

feat: add server timing to responses

Description

This PR adds server timing headers to responses by wrapping all responses returned by fetch in a Response object that includes the server timing headers.

The headers are generated by wrapping async functions with a serverTiming utility function that records the time taken to execute the function, and then adding those headers to an array on the VerifiedFetch class.

Notes & open questions

• We need to work out exactly what events we need to time
• I'd also like to clean up the serverTiming utility function usage so that it's easier to add new timings without having to handle the error and success cases manually for each one.

Example of current server timings for http://bafybeie4vcqkutumw7s26ob2bwqwqi44m6lrssjmiirlhrzhs2akdqmkw4.ipfs.helia-sw-gateway.localhost/:

Example of current server timings for http://blog-ipfs-tech.ipns.helia-sw-gateway.localhost/:

Change checklist

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation if necessary (this includes comments as well)
• I have added tests that prove my fix is effective or that my feature works