Bump version to 3.12 and update changelogs (#812) #2183

Job	Run time
Rustfmt (stable)	7s
clippy_check (ubuntu-latest, stable)	27s
Build and Test (ubuntu-latest, 1.70)	2m 22s
clippy_check (ubuntu-latest, nightly)	32s
Build and Test (ubuntu-latest, 1.75)	2m 0s
clippy_check (windows-latest, stable)	1m 2s
Build and Test (ubuntu-latest, 1.80)	1m 55s
clippy_check (windows-latest, nightly)	53s
Build and Test (ubuntu-latest, stable)	4m 20s
Build and Test (ubuntu-latest, beta)	1m 53s
Build and Test (ubuntu-latest, nightly)	50s
Build and Test (windows-latest, 1.70)	3m 13s
Build and Test (windows-latest, 1.75)	3m 14s
Build and Test (windows-latest, 1.80)	3m 15s
Build and Test (windows-latest, stable)	3m 26s
Build and Test (windows-latest, beta)	2m 51s
Build and Test (windows-latest, nightly)	1m 55s
Tests result	1s
	34m 16s

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