Remove `python-gil` requirement and enable free-threaded Python #6042

Job	Run time
build_windows (3.14)	10m 56s
build_windows (3.13)	10m 23s
build_linux (3.11)	5m 54s
build_linux (3.14)	6m 46s
build_linux (3.10)	6m 53s
build_linux (3.13)	6m 34s
build_windows (3.10)	10m 41s
build_windows (3.11)	10m 39s
build_linux (3.12)	7m 19s
build_windows (3.12)	11m 0s
test_linux (3.11, false, ubuntu-22.04)	35s
test_linux (3.12, false, ubuntu-22.04)	32s
test_linux (3.14, false, ubuntu-22.04)	33s
test_examples_linux (3.11, false, ubuntu-22.04)	9m 19s
test_linux (3.10, false, ubuntu-22.04)	36s
test_linux (3.13, false, ubuntu-22.04)	22s
upload_linux	-1s
test_windows (3.13, false, windows-latest)	4m 7s
test_windows (3.14, false, windows-latest)	4m 12s
test_windows (3.10, false, windows-latest)	4m 12s
test_windows (3.12, false, windows-latest)	4m 20s
test_windows (3.11, false, windows-latest)	4m 29s
upload_windows	-1s
Clean up anaconda packages	0s
	2h 0m 20s

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