Remove `python-gil` requirement and enable free-threaded Python #6349

Job	Run time
build_windows (3.10)	9m 46s
build_windows (3.12)	9m 8s
build_linux (3.11)	5m 56s
build_linux (3.14)	5m 47s
build_windows (3.11)	9m 4s
build_windows (3.13)	9m 33s
build_linux (3.12)	5m 58s
build_linux (3.13)	5m 58s
build_windows (3.14)	8m 48s
build_linux (3.10)	6m 10s
build_windows (3.14, 3.14.* *_cp314)	9m 15s
build_linux (3.14, 3.14.* *_cp314)	5m 57s
test_examples_linux (3.14, 3.14.* *_cp314, false, ubuntu-latest)	2m 56s
test_examples_linux (3.14, false, ubuntu-latest)	3m 0s
test_linux (3.12, false, ubuntu-latest)	1m 49s
test_linux (3.14, false, ubuntu-latest)	1m 56s
test_linux (3.10, false, ubuntu-latest)	2m 5s
test_linux (3.13, false, ubuntu-latest)	1m 52s
test_linux (3.11, false, ubuntu-latest)	2m 4s
test_linux (3.14, 3.14.* *_cp314, false, ubuntu-22.04)	1m 59s
upload_linux	-1s
test_windows (3.11, false, windows-latest)	3m 46s
test_windows (3.14, false, windows-latest)	3m 31s
test_windows (3.13, false, windows-latest)	3m 18s
test_windows (3.10, false, windows-latest)	3m 42s
test_windows (3.14, 3.14.* *_cp314, false, windows-latest)	3m 40s
test_windows (3.12, false, windows-latest)	3m 16s
upload_windows	0s
Clean up anaconda packages	-1s
	2h 10m 12s

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