improve: rework `VoiceModel` #2854

Job	Run time
build-unix-cpp-example (macos-latest, osx-x64-cpu-cpp-shared)	1m 55s
actionlint	22s
build-and-test-python-api (windows-latest)	5m 53s
build-and-test-java-api (windows-latest)	7m 38s
build-unix-cpp-example (ubuntu-latest, linux-x64-cpu-cpp-shared)	1m 35s
build-and-test-python-api (macos-latest)	3m 3s
build-and-test-java-api (macos-latest)	2m 57s
build-and-test-python-api (ubuntu-latest)	3m 12s
build-and-test-java-api (ubuntu-latest)	3m 20s
build-windows-cpp-example	4m 28s
c-header	55s
rust-integration-test-strategy-matrix	1s
rust-lint	4m 50s
rust-unit-test	5m 25s
shellcheck	20s
validate-cargo-lock	22s
rust-integration-test (macos-12)	2m 48s
rust-integration-test (ubuntu-20.04)	1m 37s
	50m 41s

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