add default for BenchArgs #205

Job	Run time
Examples Bench (ubuntu-latest)	1m 58s
Clippy (ubuntu-latest)	21s
Internals Bench (ubuntu-latest)	26s
Examples Test (ubuntu-latest, stable)	53s
Clippy (macos-latest)	17s
Internals Bench (macos-latest)	23s
Examples Bench (macos-latest)	1m 58s
Examples Test (ubuntu-latest, nightly)	1m 4s
Clippy (windows-latest)	1m 44s
Internals Bench (windows-latest)	1m 11s
Examples Bench (windows-latest)	4m 30s
Examples Test (macos-latest, stable)	47s
Examples Test (macos-latest, nightly)	1m 3s
Rustdoc	19s
Examples Test (windows-latest, stable)	2m 17s
Rustfmt	12s
Unit Test (ubuntu-latest, stable)	40s
Examples Test (windows-latest, nightly)	1m 38s
Unit Test (ubuntu-latest, nightly)	45s
Unit Test (Miri)	1m 40s
Unit Test (macos-latest, stable)	56s
Unit Test (macos-latest, nightly)	34s
Unit Test (windows-latest, stable)	1m 57s
Unit Test (windows-latest, nightly)	1m 9s
	28m 42s

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