fix(httpx): Handle cookies correctly on every request path

[Mantisus]

Description

• Unified cookie handling across all the ways HttpxHttpClient sends a request.
• Fixed possible incorrect cookie handling when the client goes through a proxy.
• Optimized header generation for HttpxHttpClient.

Testing

• Added new testing to check the processing cookies.

[Copilot]

Pull request overview

This PR updates HttpxHttpClient to unify cookie handling across request paths (including redirects and proxies) and adjusts header generation so the default “browser-like” headers come from a single sampled profile. It also reshuffles/extends unit tests to validate cookie behavior across clients and introduces a deprecation warning for HeaderGenerator.get_common_headers().

Changes:

• Reworked HttpxHttpClient request construction and transport behavior to rebuild Cookie headers per hop and to keep cookie state in Session (including when proxying).
• Updated header generation to request a consistent set of headers from HeaderGenerator.get_specific_headers() (single profile sample) and added tests around this.
• Consolidated cookie/session tests across HTTP clients and added proxy + redirect coverage; deprecated get_common_headers() with a warning and updated tests accordingly.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/unit/http_clients/test_impit.py	Removes Impit-specific cookie/session tests that were moved to shared HTTP client test coverage.
tests/unit/http_clients/test_httpx.py	Adds Httpx-specific tests for same-origin logic, proxy-kwarg behavior, and header sampling behavior.
tests/unit/http_clients/test_http_clients.py	Adds shared cookie/session behavior tests across all HTTP clients, including proxy scenarios.
tests/unit/fingerprint_suite/test_header_generator.py	Updates test to assert the new deprecation warning for get_common_headers().
src/crawlee/http_clients/_httpx.py	Implements unified cookie handling across request paths (redirects + proxies), refactors request building, and optimizes generated header selection.
src/crawlee/fingerprint_suite/_header_generator.py	Marks get_common_headers() as deprecated and emits a DeprecationWarning.

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.