Remove `python-gil` requirement and enable free-threaded Python #6046

Job	Run time
build_windows (3.12)	11m 3s
build_windows (3.14, 3.14.* *_cp314)	13m 26s
build_windows (3.13)	10m 30s
build_windows (3.11)	10m 56s
build_windows (3.14)	10m 14s
build_linux (3.14)	6m 11s
build_linux (3.14, 3.14.* *_cp314)	6m 36s
build_linux (3.13)	7m 14s
build_linux (3.12)	6m 30s
build_linux (3.10)	6m 9s
build_linux (3.11)	6m 5s
build_windows (3.10)	10m 36s
test_examples_linux (3.11, false, ubuntu-22.04)	8m 53s
upload_linux	0s
upload_windows	0s
Clean up anaconda packages	0s
	1h 54m 23s

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