Remove `python-gil` requirement and enable free-threaded Python #6151

Job	Run time
build_windows (3.11)	2m 42s
build_windows (3.10)	2m 42s
build_windows (3.13)	2m 49s
build_linux (3.11)	5m 41s
build_linux (3.14, 3.14.* *_cp314)	5m 39s
build_windows (3.14, 3.14.* *_cp314)	2m 46s
build_linux (3.10)	5m 56s
build_linux (3.14)	5m 40s
build_linux (3.13)	5m 36s
build_windows (3.12)	2m 53s
build_windows (3.14)	2m 48s
build_linux (3.12)	5m 31s
test_windows	-1s
upload_windows	-1s
test_examples_linux (3.11, false, ubuntu-22.04)	9m 33s
test_linux (3.13, false, ubuntu-22.04)	2m 59s
test_linux (3.11, false, ubuntu-22.04)	3m 0s
test_linux (3.10, false, ubuntu-22.04)	3m 9s
test_linux (3.14, false, ubuntu-22.04)	4m 27s
test_linux (3.12, false, ubuntu-22.04)	4m 25s
test_linux (3.14, 3.14.* *_cp314, false, ubuntu-22.04)	2m 55s
upload_linux	0s
Clean up anaconda packages	0s
	1h 21m 9s

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