Remove `python-gil` requirement and enable free-threaded Python #6350

Job	Run time
build_linux (3.11)	5m 4s
build_linux (3.10)	5m 39s
build_windows (3.13)	9m 1s
build_windows (3.14, 3.14.* *_cp314)	8m 54s
build_windows (3.14)	9m 52s
build_windows (3.10)	8m 36s
build_windows (3.12)	10m 18s
build_linux (3.14, 3.14.* *_cp314)	5m 9s
build_linux (3.14)	5m 43s
build_linux (3.13)	5m 32s
build_windows (3.11)	8m 11s
build_linux (3.12)	5m 36s
test_examples_linux (3.14, false, ubuntu-latest)	6m 9s
test_linux (3.12, false, ubuntu-latest)	2m 52s
test_linux (3.10, false, ubuntu-latest)	3m 39s
test_linux (3.13, false, ubuntu-latest)	2m 45s
test_examples_linux (3.14, 3.14.* *_cp314, false, ubuntu-latest)	5m 12s
test_linux (3.14, 3.14.* *_cp314, false, ubuntu-22.04)	2m 59s
test_linux (3.11, false, ubuntu-latest)	3m 19s
test_linux (3.14, false, ubuntu-latest)	3m 9s
upload_linux	0s
test_windows (3.10, false, windows-latest)	1h 0m 3s
test_windows (3.13, false, windows-latest)	1h 0m 3s
test_windows (3.11, false, windows-latest)	3m 59s
test_windows (3.14, false, windows-latest)	4m 10s
test_windows (3.14, 3.14.* *_cp314, false, windows-latest)	4m 11s
test_windows (3.12, false, windows-latest)	3m 44s
Clean up anaconda packages	0s
upload_windows	0s
	4h 13m 49s

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