feat: add perf walltime support #106

Job	Run time
cmake-integration-tests (instrumentation, ubuntu-latest)	1m 19s
tests	16s
cmake-integration-tests (walltime, codspeed-macro)	2m 12s
cmake-integration-tests (off, ubuntu-latest)	56s
bazel-integration-tests (walltime, codspeed-macro)	33s
bazel-integration-tests (off, ubuntu-latest)	17s
bazel-integration-tests (instrumentation, ubuntu-latest)	16s
	5m 49s

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