build(deps): Replace httpx with httpx2 (DM-4106)

[haakonvt]

Summary

Migrate SDK from unmaintained httpx to httpx2 to resolve e.g. authlib deprecation warnings.

Changes

• Dependencies: Replace httpx with httpx2 and pytest-httpx with httpx2-pytest.
• Pyodide: Clean up legacy pyodide-httpx patches in favor of native httpx2 browser transport (httpx2-jsfetch).

[gemini-code-assist]

Code Review

This pull request migrates the SDK's underlying HTTP library from httpx to httpx2 across the codebase and test suites. A critical issue was found in the Pyodide patching helper where calling get_global_async_httpx_client directly can raise a RuntimeError if no event loop is running, which can be resolved by dynamically wrapping the client getter.

[codecov]

Codecov Report

❌ Patch coverage is 96.89922% with 24 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.12%. Comparing base (3556792) to head (2fec008).

Files with missing lines	Patch %	Lines
tests/tests_unit/test_api/test_functions.py	87.69%	8 Missing ⚠️
cognite/client/utils/_pyodide_helpers.py	0.00%	6 Missing ⚠️
tests/tests_unit/test_api/test_relationships.py	78.57%	3 Missing ⚠️
cognite/client/utils/_version_checker.py	0.00%	2 Missing ⚠️
tests/tests_unit/test_api/test_entity_matching.py	84.61%	2 Missing ⚠️
tests/tests_unit/test_api/test_events.py	83.33%	2 Missing ⚠️
cognite/client/_basic_api_client.py	83.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2818      +/-   ##
==========================================
+ Coverage   93.09%   93.12%   +0.03%     
==========================================
  Files         516      516              
  Lines       53722    53707      -15     
==========================================
+ Hits        50012    50017       +5     
+ Misses       3710     3690      -20     

Files with missing lines	Coverage Δ
cognite/client/_http_client.py	93.42% <100.00%> (ø)
cognite/client/exceptions.py	94.84% <100.00%> (ø)
cognite/client/response.py	75.45% <100.00%> (ø)
cognite/client/utils/_concurrency.py	93.75% <ø> (ø)
cognite/client/utils/_uploading.py	72.30% <100.00%> (ø)
...tests_integration/test_api/test_jupyter_interop.py	100.00% <ø> (ø)
tests/tests_unit/test_api/test_3d.py	100.00% <100.00%> (ø)
tests/tests_unit/test_api/test_agents.py	100.00% <100.00%> (ø)
tests/tests_unit/test_api/test_agents_actions.py	100.00% <100.00%> (ø)
tests/tests_unit/test_api/test_agents_chat.py	100.00% <100.00%> (ø)
... and 44 more

... and 6 files with indirect coverage changes

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[audunska]

I looked very carefully at all the changes, especially fdc026c
Guaranteed to be bug free.

[haakonvt]

[audunska]

"I completely understand all the pyodide dependency hacking"

[haakonvt]

🦄

[haakonvt]

🦄