Introduce Python 3.14 compatibility #3790

Job	Run time
smoke (amaranth-lang/amaranth-stdio)	58s
check-links	1m 2s
smoke (amaranth-lang/amaranth-soc)	59s
smoke (amaranth-lang/amaranth-boards)	36s
test (3.11)	2m 51s
test (3.10)	2m 36s
test (pypy-3.9)	6m 15s
test (3.15-dev)	7s
test (3.12)	5m 26s
test (3.13)	3m 49s
test (3.14)	4m 0s
document	56s
test (pypy-3.10)	5m 50s
test (3.9)	3m 54s
test (pypy-3.11)	4m 20s
publish-docs	7s
publish-docs-dev	-1s
required	2s
publish-schemas	7s
publish-package	17s
publish-release	0s
	44m 11s

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