feat(plugins): Remove deprecated `SerializationPluginProtocol` #4875

Job	Run time
slotscheck	18s
pyright	38s
validate	15s
Test server integration (uvicorn<0.27.0)	39s
mypy	58s
Test server integration (uvicorn>=0.27.0)	36s
Test Minimal Application with Base Dependencies	13s
Test Minimal Pydantic 1 application	25s
test-platform-compat	0s
test (3.10) / test	1m 34s
test (3.11) / test	1m 27s
test (3.12) / test	2m 35s
test (3.13) / test	1m 25s
test (3.9) / test	2m 13s
build-docs	1m 19s
test_success	1s
upload-test-coverage	16s
codeql	2m 18s
sonar	1m 13s
	18m 23s

Provide feedback