docs: add advanced query parameters guide with qs_codec usage

[techouse]

Summary

This pull request is a followup on #3642 and adds comprehensive documentation for advanced query parameter handling in HTTPX. The new guide explains how to use the third-party qs_codec package to encode and decode complex query strings, including nested dictionaries, lists, and duplicate keys. It also provides practical examples and a custom transport for merging query parameters.

New advanced query parameter documentation:

• Added a detailed guide (docs/advanced/query_parameters.md) on handling complex/nested query parameters in HTTPX using the qs_codec package, including encoding/decoding, list formats, space encoding modes, and merging strategies.
• Included code examples demonstrating usage of qs_codec for encoding nested data, handling repeated keys, and customizing percent-encoding.

Practical usage and integration:

• Provided a helper function and a custom HTTPX transport (SmartQueryStrings) to automatically merge additional query parameters with existing ones, showcasing real-world integration patterns.
• Explained real-world usage with the Strapi CMS and referenced the strapi-client package for further implementation details.

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.

[karpetrosyan]

I would recommend to isolate it in a standalone repo, instead of documenting bunch of custom code. So a user can just import that transport and add it to his chain of transports.
httpx-qs for example

[techouse]

httpx-qs

@karpetrosyan makes sense. I probably shouldn't wait for httpx v1, right?

[karpetrosyan]

I have no context about v1, but I’d expect it to be pretty straightforward to port transports to the v1-compatible API.

[techouse]

I would recommend to isolate it in a standalone repo, instead of documenting bunch of custom code. So a user can just import that transport and add it to his chain of transports. httpx-qs for example

Done! 😇 https://pypi.org/project/httpx-qs/