feat: add perf walltime support #144

Job	Run time
tests	18s
cmake-integration-tests (instrumentation, ubuntu-latest)	1m 29s
bazel-integration-tests (walltime, codspeed-macro)	2m 30s
cmake-integration-tests (off, ubuntu-latest)	1m 9s
bazel-integration-tests (off, ubuntu-latest)	35s
bazel-integration-tests (instrumentation, ubuntu-latest)	1m 45s
windows-bazel-build (off)	32s
windows-bazel-build (walltime)	36s
windows-cmake-build (off)	39s
cmake-integration-tests (walltime, codspeed-macro)	3m 16s
windows-cmake-build (walltime)	41s
	13m 30s

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