Fix content negotiation

[martincostello]

Fix inability to return different responses based on content negotiation via HTTP request headers by including a hash of their names and values in the key for the registration.

---

As per the test, I found this while doing some work where I needed to intercept responses to the GitHub API. The Get a pull request has a behaviour where different values for the Accept header change the format of the response.

I had the need to get the JSON representation of a pull request and the diff for it in the same operation. This isn't currently possible using the "simple" API as the HTTP request headers aren't taken into account when storing the interception registrations, which created a Last-One-Wins situation meaning you couldn't have a response for the same HTTP method and URL.

While it was possible using the For() overloads, this has the user fall off a cliff in terms of usability and needs them to write all the matching logic themselves.

In addition to the key changes, the collections used for header collections weren't being copied, meaning that the values also got mutated by reference when the user changed the registration. This part could potentially be a breaking behaviour change if someone is mutating a builder post-request expecting the matched values to change, but I don't think that's the behaviour originally intended in the design so is accidental.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.32%. Comparing base (32d486a) to head (a7ed243).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1009      +/-   ##
==========================================
+ Coverage   99.30%   99.32%   +0.01%     
==========================================
  Files          15       15              
  Lines         868      886      +18     
  Branches      198      204       +6     
==========================================
+ Hits          862      880      +18     
  Misses          4        4              
  Partials        2        2              

Flag	Coverage Δ
linux	99.32% <100.00%> (+0.01%)	⬆️
macos	99.32% <100.00%> (+0.01%)	⬆️
windows	99.32% <100.00%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[martincostello]

Tested the changes in the app where I found this, and with the build from the PR it works as I'd expect now: martincostello/costellobot#2068

[Copilot]

Copilot reviewed 3 out of 3 changed files in this pull request and generated 5 comments.