feat: add perf walltime support #148

Job	Run time
tests	25s
cmake-integration-tests (instrumentation, ubuntu-latest)	1m 27s
cmake-integration-tests (walltime, codspeed-macro)	3m 35s
windows-bazel-build (off)	1m 21s
cmake-integration-tests (off, ubuntu-latest)	1m 9s
windows-cmake-build (off)	48s
windows-bazel-build (walltime)	1m 31s
windows-cmake-build (walltime)	50s
bazel-integration-tests (walltime, codspeed-macro)	2m 29s
bazel-integration-tests (instrumentation, ubuntu-latest)	1m 12s
bazel-integration-tests (off, ubuntu-latest)	36s
	15m 23s

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