feat: add perf walltime support #149

Job	Run time
bazel-integration-tests (instrumentation, ubuntu-latest)	1m 11s
tests	11s
bazel-integration-tests (walltime, codspeed-macro)	2m 32s
windows-cmake-build (walltime)	2m 16s
cmake-integration-tests (instrumentation, ubuntu-latest)	1m 37s
windows-cmake-build (off)	2m 37s
bazel-integration-tests (off, ubuntu-latest)	31s
cmake-integration-tests (walltime, codspeed-macro)	3m 15s
cmake-integration-tests (off, ubuntu-latest)	1m 0s
windows-bazel-build (off)	2m 8s
windows-bazel-build (walltime)	1m 51s
	19m 9s

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