feat: Replace zstandard with backports.zstd for better compatibility with Python3.14+ #6820

Job	Run time
pyright	31s
Test Minimal Application with Base Dependencies	18s
slotscheck	17s
validate	20s
mypy	41s
test_typing_extensions (latest)	21s
test_typing_extensions (4.13.1)	23s
Test server integration (uvicorn<0.27.0)	45s
test_typing_extensions (4.14.0)	19s
Test server integration (uvicorn>=0.27.0)	52s
test_typing_extensions (4.12.1)	20s
test (3.11) / test	2m 19s
test (3.13) / test	2m 14s
test (3.12) / test	2m 32s
test (3.14) / test	2m 11s
test-platform-compat	0s
build-docs	2m 37s
test_success	3s
upload-test-coverage	20s
	17m 23s

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