Remove `python-gil` requirement and enable free-threaded Python #6353

Job	Run time
build_windows (3.14)	7m 40s
build_windows (3.11)	9m 39s
build_linux (3.14, 3.14.* *_cp314)	6m 19s
build_linux (3.13)	6m 14s
build_linux (3.11)	6m 15s
build_windows (3.12)	9m 16s
build_linux (3.14)	5m 40s
build_linux (3.12)	5m 42s
build_linux (3.10)	5m 37s
build_windows (3.10)	8m 28s
build_windows (3.13)	8m 14s
build_windows (3.14, 3.14.* *_cp314)	8m 20s
test_examples_linux (3.14, 3.14.* *_cp314, false, ubuntu-latest)	57s
test_examples_linux (3.14, false, ubuntu-latest)	56s
test_linux (3.13, false, ubuntu-latest)	32s
test_linux (3.14, false, ubuntu-latest)	44s
test_linux (3.12, false, ubuntu-latest)	36s
test_linux (3.11, false, ubuntu-latest)	45s
test_linux (3.10, false, ubuntu-latest)	44s
test_linux (3.14, 3.14.* *_cp314, false, ubuntu-22.04)	46s
upload_linux	-1s
test_windows (3.11, false, windows-latest)	3m 49s
test_windows (3.10, false, windows-latest)	3m 44s
test_windows (3.13, false, windows-latest)	3m 41s
test_windows (3.14, 3.14.* *_cp314, false, windows-latest)	3m 10s
test_windows (3.12, false, windows-latest)	3m 41s
test_windows (3.14, false, windows-latest)	3m 36s
upload_windows	0s
Clean up anaconda packages	0s
	1h 55m 4s

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