feat: added subprocess test client #4547

Job	Run time
mypy	1m 5s
pyright	39s
slotscheck	23s
Test server integration (uvicorn<0.27.0)	35s
Test Minimal Application with Base Dependencies	14s
Test server integration (uvicorn>=0.27.0)	42s
Test Minimal Pydantic 1 application	14s
validate	20s
test-platform-compat	0s
test (3.10) / test	1m 48s
test (3.11) / test	1m 39s
test (3.12) / test	1m 57s
test (3.8) / test	1m 57s
test (3.9) / test	1m 54s
build-docs	0s
codeql	0s
upload-test-coverage	0s
sonar	0s
	13m 27s

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