Remove `python-gil` requirement and enable free-threaded Python #6354

Job	Run time
build_windows (3.11)	8m 39s
build_windows (3.13)	9m 23s
build_windows (3.14)	8m 42s
build_linux (3.10)	6m 34s
build_linux (3.12)	5m 12s
build_windows (3.12)	8m 13s
build_linux (3.14)	5m 26s
build_linux (3.13)	5m 1s
build_linux (3.11)	5m 6s
build_linux (3.14, 3.14.* *_cp314)	5m 8s
build_windows (3.10)	8m 29s
build_windows (3.14, 3.14.* *_cp314)	9m 5s
test_examples_linux (3.14, 3.14.* *_cp314, false, ubuntu-latest)	5m 10s
test_linux (3.14, false, ubuntu-latest)	3m 22s
test_linux (3.10, false, ubuntu-latest)	3m 3s
test_examples_linux (3.14, false, ubuntu-latest)	5m 10s
test_linux (3.13, false, ubuntu-latest)	3m 15s
test_linux (3.11, false, ubuntu-latest)	3m 4s
test_linux (3.12, false, ubuntu-latest)	3m 2s
test_linux (3.14, 3.14.* *_cp314, false, ubuntu-22.04)	2m 53s
test_windows (3.13, false, windows-latest)	3m 41s
test_windows (3.12, false, windows-latest)	3m 17s
test_windows (3.14, 3.14.* *_cp314, false, windows-latest)	3m 33s
test_windows (3.11, false, windows-latest)	3m 12s
test_windows (3.14, false, windows-latest)	3m 32s
test_windows (3.10, false, windows-latest)	4m 22s
upload_linux	-1s
upload_windows	0s
Clean up anaconda packages	0s
	2h 15m 33s

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