`Synthesizer::new`を非asyncにする #2246

Job	Run time
shellcheck	18s
validate-cargo-lock	2m 10s
actionlint	16s
build-and-test-java-api (windows-latest)	7m 18s
build-and-test-python-api (windows-latest)	6m 1s
build-and-test-java-api (macos-latest)	4m 19s
build-and-test-python-api (macos-latest)	4m 21s
build-and-test-java-api (ubuntu-latest)	3m 57s
build-and-test-python-api (ubuntu-latest)	2m 30s
build-unix-cpp-example (macos-latest, osx-x64-cpu-cpp-shared)	4m 8s
build-unix-cpp-example (ubuntu-latest, linux-x64-cpu-cpp-shared)	3m 11s
build-windows-cpp-example	4m 12s
c-header	2m 5s
rust-integration-test-strategy-matrix	3s
rust-lint	4m 8s
rust-unit-test	5m 27s
rust-integration-test (windows-2019, directml)	4m 1s
rust-integration-test (macos-11)	2m 35s
rust-integration-test (ubuntu-20.04)	1m 5s
	1h 2m 5s

Provide feedback