feat: allow configuring `NewDecoder` via callbacks #12

Job	Run time
verify-and-test (1.19, ubuntu-latest)	46s
verify-and-test (1.19, macos-latest)	52s
verify-and-test (1.19, windows-latest)	2m 37s
verify-and-test (1.20, ubuntu-latest)	1m 2s
verify-and-test (1.20, macos-latest)	3m 59s
verify-and-test (1.20, windows-latest)	3m 30s
	12m 46s

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