Add fd table to RuntimeImpl and TestRuntime #672

Job	Run time
rust_ci (ubuntu-latest, stable)	1m 29s
rust_ci (macos-latest, beta)	1m 31s
rust_ci (ubuntu-latest, beta)	1m 27s
rust_ci (macos-latest, stable)	1m 41s
rust_ci (windows-latest, beta)	2m 43s
rust_ci (windows-latest, stable)	2m 51s
	11m 42s

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