Add benchmarking mode to exrmetrics #2353

Job	Run time
macOS.1: Release / steps	8m 18s
macOS.3: static / steps	9m 15s
macOS.4: threads=OFF / steps	7m 47s
macOS.2: Debug / steps	20m 25s
macOS.5: pkgconfig=OFF, examples=OFF, tools=OFF, docs=OFF, internal imath+deflate / steps	1m 25s
macOS.6: macos-13 / steps	20m 9s
Windows.1: Release / steps	14m 49s
Windows.2: Debug / steps	42m 6s
Windows.3: static / steps	13m 20s
Windows.4: threads=OFF / steps	13m 28s
Windows.5: pkgconfig=OFF, examples=OFF, tools=OFF, docs=OFF, internal imath+deflate / steps	1m 51s
Windows.6: vfx2022 / steps	14m 8s
Linux.1: Release / steps	4m 36s
Linux.2: Debug / steps	4m 35s
Linux.3: static / steps	4m 34s
Linux.4: threads=OFF / steps	4m 34s
Linux.5: pkgconfig=OFF, examples=OFF, tools=OFF, docs=OFF, internal deflate / steps	4m 10s
Linux.6: custom namespace / steps	4m 30s
Linux.7: clang / steps	4m 33s
Linux.8: vfx2023 / steps	4m 33s
	3h 23m 6s

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