chore: replace `respx` mocks with `pytest-httpserver` in tests #329

Job	Run time
Lint check / Lint check (3.10)	10s
Lint check / Lint check (3.9)	12s
Type check / Type check (3.9)	19s
Lint check / Lint check (3.13)	9s
Lint check / Lint check (3.12)	11s
Lint check / Lint check (3.11)	11s
Type check / Type check (3.13)	16s
Type check / Type check (3.12)	21s
Type check / Type check (3.11)	15s
Docs check / Docs check	1m 1s
Type check / Type check (3.10)	19s
Unit tests / Unit tests (ubuntu-latest, 3.9)	39s
Async dostrings check / Async docstrings check	18s
Unit tests / Unit tests (ubuntu-latest, 3.11)	41s
Unit tests / Unit tests (ubuntu-latest, 3.10)	40s
Unit tests / Unit tests (ubuntu-latest, 3.13)	36s
Unit tests / Unit tests (ubuntu-latest, 3.12)	36s
Unit tests / Unit tests (windows-latest, 3.11)	1m 8s
Unit tests / Unit tests (windows-latest, 3.12)	1m 7s
Unit tests / Unit tests (windows-latest, 3.10)	58s
Unit tests / Unit tests (windows-latest, 3.9)	53s
Unit tests / Unit tests (windows-latest, 3.13)	1m 6s
Integration tests / Approve integration tests for PRs from forks	3s
Integration tests / Integration tests	0s
Integration tests / Integration tests for PRs from forks	0s
	12m 9s

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