Bump version to 3.12 and update changelogs #2182

Job	Run time
Rustfmt (stable)	12s
Build and Test (ubuntu-latest, 1.70)	2m 19s
clippy_check (ubuntu-latest, stable)	24s
Build and Test (ubuntu-latest, 1.75)	2m 10s
Build and Test (ubuntu-latest, 1.80)	2m 4s
clippy_check (ubuntu-latest, nightly)	26s
Build and Test (ubuntu-latest, stable)	4m 19s
clippy_check (windows-latest, stable)	2m 4s
Build and Test (ubuntu-latest, beta)	1m 52s
clippy_check (windows-latest, nightly)	59s
Build and Test (ubuntu-latest, nightly)	48s
Build and Test (windows-latest, 1.70)	3m 1s
Build and Test (windows-latest, 1.75)	3m 0s
Build and Test (windows-latest, 1.80)	3m 0s
Build and Test (windows-latest, stable)	4m 23s
Build and Test (windows-latest, beta)	3m 22s
Build and Test (windows-latest, nightly)	1m 46s
Tests result	1s
	36m 10s

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