Remove `python-gil` requirement and enable free-threaded Python #6041

Job	Run time
build_windows (3.10)	11m 4s
build_linux (3.14)	6m 43s
build_windows (3.12)	10m 58s
build_windows (3.14)	11m 8s
build_linux (3.10)	6m 9s
build_windows (3.11)	11m 18s
build_windows (3.13)	11m 14s
build_linux (3.13)	6m 51s
build_linux (3.12)	6m 55s
build_linux (3.11)	6m 31s
test_linux (3.13, false, ubuntu-22.04)	3m 26s
test_linux (3.12, false, ubuntu-22.04)	3m 25s
test_linux (3.11, false, ubuntu-22.04)	3m 14s
test_examples_linux (3.11, false, ubuntu-22.04)	9m 33s
test_linux (3.14, false, ubuntu-22.04)	3m 22s
test_linux (3.10, false, ubuntu-22.04)	3m 25s
upload_linux	0s
test_windows (3.11, false, windows-latest)	5m 8s
test_windows (3.14, false, windows-latest)	4m 0s
test_windows (3.10, false, windows-latest)	4m 46s
test_windows (3.13, false, windows-latest)	4m 37s
test_windows (3.12, false, windows-latest)	4m 3s
upload_windows	-1s
Clean up anaconda packages	0s
	2h 17m 49s

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