Build up request query parameters from URL client and request parameters

[KeeganOP]

Summary

Fixes #905 - Currently the URL params are extracted but never added to the request params. This PR uses those params as a base and merges the params specified on the client and request (in that order) and passes that as the final request params

Checklist

• I understand that this PR may be closed in case there was no previous discussion. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.

[codspeed-hq]

Merging this PR will not alter performance

✅ 7 untouched benchmarks

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_{Comparing KeeganOP:main (643ad3f) with main (8a903c6)}

[mbeijen]

I think this should be fixed in init and not here - because this would still not work with your code:

httpx2.Request("GET", "http://example.com/?a=1", params={"b": "2"})

I fixed this in httpxyz like so:
https://codeberg.org/httpxyz/httpxyz/commit/417d6c6fa193c5f29cdacefef6a4f7c9e5d30313