Remove `python-gil` requirement and enable free-threaded Python #6301

Job	Run time
build_linux (3.11)	5m 19s
build_linux (3.13)	5m 35s
build_windows (3.14)	9m 49s
build_windows (3.10)	9m 20s
build_windows (3.12)	8m 7s
build_windows (3.13)	8m 9s
build_linux (3.14, 3.14.* *_cp314)	5m 31s
build_linux (3.14)	5m 21s
build_windows (3.11)	9m 19s
build_linux (3.10)	5m 32s
build_linux (3.12)	5m 50s
build_windows (3.14, 3.14.* *_cp314)	8m 28s
test_examples_linux (3.11, false, ubuntu-latest)	5m 19s
test_linux (3.12, false, ubuntu-latest)	2m 5s
test_linux (3.11, false, ubuntu-latest)	2m 7s
test_linux (3.10, false, ubuntu-latest)	2m 42s
test_linux (3.14, false, ubuntu-latest)	2m 16s
test_linux (3.13, false, ubuntu-latest)	2m 19s
test_linux (3.14, 3.14.* *_cp314, false, ubuntu-22.04)	2m 25s
upload_linux	-1s
test_windows (3.13, false, windows-latest)	3m 32s
test_windows (3.12, false, windows-latest)	4m 0s
test_windows (3.14, false, windows-latest)	4m 25s
test_windows (3.10, false, windows-latest)	3m 56s
test_windows (3.11, false, windows-latest)	3m 22s
test_windows (3.14, 3.14.* *_cp314, false, windows-latest)	3m 55s
upload_windows	0s
Clean up anaconda packages	0s
	2h 8m 42s

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