Remove `python-gil` requirement and enable free-threaded Python #6324

Job	Run time
build_windows (3.10)	9m 13s
build_windows (3.12)	9m 35s
build_linux (3.12)	6m 23s
build_linux (3.11)	5m 12s
build_linux (3.14)	5m 19s
build_linux (3.13)	4m 37s
build_linux (3.14, 3.14.* *_cp314)	4m 39s
build_windows (3.13)	8m 45s
build_windows (3.11)	9m 22s
build_linux (3.10)	4m 45s
build_windows (3.14)	8m 33s
build_windows (3.14, 3.14.* *_cp314)	9m 49s
test_examples_linux (3.14, false, ubuntu-latest)	4m 28s
test_examples_linux (3.14, 3.14.* *_cp314, false, ubuntu-latest)	4m 32s
test_linux (3.12, false, ubuntu-latest)	2m 29s
test_linux (3.14, 3.14.* *_cp314, false, ubuntu-22.04)	2m 41s
test_linux (3.10, false, ubuntu-latest)	2m 34s
test_linux (3.13, false, ubuntu-latest)	2m 31s
test_linux (3.14, false, ubuntu-latest)	2m 34s
test_linux (3.11, false, ubuntu-latest)	2m 21s
upload_linux	0s
test_windows (3.14, 3.14.* *_cp314, false, windows-latest)	3m 42s
test_windows (3.11, false, windows-latest)	3m 49s
test_windows (3.13, false, windows-latest)	3m 26s
test_windows (3.14, false, windows-latest)	3m 36s
test_windows (3.12, false, windows-latest)	3m 35s
test_windows (3.10, false, windows-latest)	3m 43s
upload_windows	0s
Clean up anaconda packages	0s
	2h 12m 13s

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