chore(api)!: Model .fromJson() Refactor #1842

Job	Run time
test / test-dart-vm (3.0.1)	2m 8s
test / test-dart-vm (stable)	2m 26s
dart2js_test / test-dart-2js (3.0.1, chrome)	4m 38s
dart2js_test / test-dart-2js (3.0.1, firefox)	4m 25s
native_test / test-dart-native (macos-latest)	3m 57s
dart2js_test / test-dart-2js (stable, chrome)	4m 32s
ddc_test / test-dart-ddc (3.0.1, chrome)	3m 29s
native_test / test-dart-native (windows-latest)	4m 23s
dart2js_test / test-dart-2js (stable, firefox)	4m 22s
ddc_test / test-dart-ddc (3.0.1, firefox)	3m 33s
ddc_test / test-dart-ddc (stable, chrome)	3m 36s
ddc_test / test-dart-ddc (stable, firefox)	3m 53s
	45m 22s

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