Remove `python-gil` requirement and enable free-threaded Python #6181

Job	Run time
build_windows (3.14, 3.14.* *_cp314)	10m 51s
build_windows (3.12)	11m 57s
build_windows (3.11)	9m 47s
build_windows (3.10)	11m 9s
build_linux (3.10)	6m 27s
build_windows (3.14)	13m 39s
build_linux (3.12)	6m 32s
build_linux (3.14, 3.14.* *_cp314)	6m 25s
build_linux (3.13)	6m 10s
build_linux (3.11)	7m 23s
build_windows (3.13)	9m 35s
build_linux (3.14)	6m 41s
test_examples_linux (3.11, false, ubuntu-22.04)	9m 22s
test_linux (3.12, false, ubuntu-22.04)	4m 50s
test_linux (3.14, false, ubuntu-22.04)	3m 56s
test_linux (3.10, false, ubuntu-22.04)	3m 30s
test_linux (3.11, false, ubuntu-22.04)	4m 51s
test_linux (3.13, false, ubuntu-22.04)	3m 41s
test_linux (3.14, 3.14.* *_cp314, false, ubuntu-22.04)	4m 3s
upload_linux	0s
test_windows (3.10, false, windows-latest)	4m 3s
test_windows (3.13, false, windows-latest)	4m 23s
test_windows (3.12, false, windows-latest)	4m 14s
test_windows (3.11, false, windows-latest)	5m 0s
test_windows (3.14, false, windows-latest)	4m 57s
test_windows (3.14, 3.14.* *_cp314, false, windows-latest)	4m 35s
upload_windows	0s
Clean up anaconda packages	0s
	2h 48m 1s

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