feat: added subprocess test client #4577

Job	Run time
validate	17s
slotscheck	23s
pyright	38s
mypy	59s
Test Minimal Application with Base Dependencies	14s
Test server integration (uvicorn<0.27.0)	34s
Test Minimal Pydantic 1 application	16s
test-platform-compat	0s
Test server integration (uvicorn>=0.27.0)	39s
test (3.11) / test	1m 42s
test (3.10) / test	2m 8s
test (3.12) / test	3m 0s
test (3.8) / test	2m 51s
test (3.9) / test	1m 44s
build-docs	2m 15s
codeql	1m 49s
upload-test-coverage	14s
sonar	0s
	19m 43s

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