chore: replace `respx` mocks with `pytest-httpserver` in tests #323

Job	Run time
Lint check / Lint check (3.10)	10s
Lint check / Lint check (3.9)	7s
Lint check / Lint check (3.11)	7s
Lint check / Lint check (3.12)	11s
Lint check / Lint check (3.13)	7s
Async dostrings check / Async docstrings check	13s
Unit tests / Unit tests (ubuntu-latest, 3.12)	39s
Docs check / Docs check	1m 6s
Unit tests / Unit tests (ubuntu-latest, 3.13)	42s
Unit tests / Unit tests (ubuntu-latest, 3.9)	38s
Unit tests / Unit tests (windows-latest, 3.10)	1m 38s
Unit tests / Unit tests (windows-latest, 3.9)	1m 20s
Unit tests / Unit tests (windows-latest, 3.11)	1m 50s
Unit tests / Unit tests (ubuntu-latest, 3.11)	38s
Type check / Type check (3.9)	19s
Unit tests / Unit tests (windows-latest, 3.13)	1m 49s
Type check / Type check (3.13)	16s
Type check / Type check (3.10)	16s
Type check / Type check (3.12)	17s
Unit tests / Unit tests (windows-latest, 3.12)	1m 48s
Unit tests / Unit tests (ubuntu-latest, 3.10)	39s
Type check / Type check (3.11)	16s
Integration tests	0s
	15m 6s

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