refactor: `mod inner`を削除 (#897) #3248

Job	Run time
actionlint	16s
rust-integration-test-strategy-matrix	1s
rust-lint	4m 6s
rust-unit-test	7m 12s
shellcheck	13s
validate-cargo-lock	22s
build-and-test-java-api (windows-latest)	7m 58s
build-and-test-java-api (macos-latest)	2m 50s
build-and-test-python-api (windows-latest)	9m 54s
build-unix-cpp-example (macos-latest, osx-x64-cpu-cpp-shared)	1m 54s
build-and-test-java-api (ubuntu-latest)	2m 59s
build-and-test-python-api (macos-latest)	4m 16s
build-unix-cpp-example (ubuntu-latest, linux-x64-cpu-cpp-shared)	2m 56s
build-and-test-python-api (ubuntu-latest)	3m 41s
c-header	48s
build-windows-cpp-example	4m 15s
rust-integration-test (macos-13)	2m 42s
rust-integration-test (ubuntu-20.04)	1m 53s
	58m 16s

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