split decoder into spectrogram and vocoder without changing API #2992

Job	Run time
actionlint	16s
rust-unit-test	5m 17s
shellcheck	12s
rust-lint	3m 42s
validate-cargo-lock	21s
build-and-test-java-api (windows-latest)	5m 44s
build-and-test-java-api (macos-latest)	2m 41s
build-and-test-java-api (ubuntu-latest)	2m 48s
build-and-test-python-api (windows-latest)	5m 41s
build-and-test-python-api (macos-latest)	3m 8s
build-and-test-python-api (ubuntu-latest)	2m 58s
build-unix-cpp-example (macos-latest, osx-x64-cpu-cpp-shared)	1m 32s
build-unix-cpp-example (ubuntu-latest, linux-x64-cpu-cpp-shared)	1m 45s
build-windows-cpp-example	4m 2s
c-header	44s
rust-integration-test-strategy-matrix	1s
rust-integration-test (macos-12)	2m 34s
rust-integration-test (ubuntu-20.04)	1m 39s
	45m 5s

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