feat: add perf walltime support #147

Job	Run time
tests	21s
cmake-integration-tests (instrumentation, ubuntu-latest)	1m 40s
cmake-integration-tests (walltime, codspeed-macro)	3m 38s
windows-cmake-build (off)	58s
cmake-integration-tests (off, ubuntu-latest)	1m 4s
bazel-integration-tests (instrumentation, ubuntu-latest)	1m 49s
windows-cmake-build (walltime)	1m 1s
bazel-integration-tests (walltime, codspeed-macro)	2m 29s
bazel-integration-tests (off, ubuntu-latest)	33s
windows-bazel-build (off)	1m 49s
windows-bazel-build (walltime)	2m 17s
	17m 39s

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