Add set_query_pair method to UrlExt trait

[jhendrixMSFT]

A convenience method for setting query parameter key/value pairs that will overwrite an existing key with the new value.

Fixes #1907

[Copilot]

Pull Request Overview

This PR adds a new set_query_pair method to the UrlExt trait to simplify setting query parameter key/value pairs with automatic overwriting of existing values.

Key changes:

• Added UrlExt::set_query_pair() method that overwrites existing query parameters with the same key
• Comprehensive test coverage including edge cases like duplicate keys, special characters, and method chaining
• Updated CHANGELOG to document the new feature

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
sdk/core/typespec_client_core/src/http/mod.rs	Added set_query_pair() method to UrlExt trait with implementation and comprehensive tests
sdk/core/typespec_client_core/CHANGELOG.md	Documented the new UrlExt::set_query_pair() method under Features Added

[github-actions]

API Change Check

APIView identified API level changes in this PR and created the following API reviews

typespec_client_core

[heaths]

Code seems fine if only calling once, but I suspect that isn't the case.

[heaths]

I like the shape of the API, but you're not going to be able to use string slices into the Url once you start manipulating. You'll need to call into_owned() for each key and value like we were before, or clone the Url to use slices which might be cheaper - certainly less fragmented - but @LarryOsterman doesn't think that it's much of an issue on Windows and linux, at least, these days. So maybe we don't need to over-optimize now as long as we make sure the API could work either way.

But since when did order matter? The existing way we use in client methods doesn't preserve order. Params we keep end up first and params we replace/add end up coming last. This seems like a new and unnecessary requirement, and one I don't think other languages do. It shouldn't matter anyway except maybe for array params to combine them in order LTR.