Add API: `make_proxy_observed` #24

Job	Run time
Run BVT with Intel oneAPI / bvt-oneapi	9m 49s
Run BVT with Clang / bvt-clang	9m 34s
Run BVT with NVHPC / bvt-nvhpc	13m 23s
Run BVT with MSVC / bvt-msvc	10m 33s
Run BVT with GCC / bvt-gcc	8m 35s
Run BVT for compatibility / bvt-compatibility (clang, 19, false)	2m 57s
Run BVT with AppleClang / bvt-appleclang	7m 55s
Build mkdocs / bvt-mkdocs	22s
Run BVT for compatibility / bvt-compatibility (gcc, 14, true)	1m 49s
Run BVT for compatibility / bvt-compatibility (clang, 20, true)	2m 43s
Run BVT for compatibility / bvt-compatibility (gcc, 13, false)	1m 31s
Run BVT for compatibility / bvt-compatibility (clang, 18, false)	3m 15s
Run BVT for compatibility / bvt-compatibility (clang, 17, false)	3m 15s
Run BVT for compatibility / bvt-compatibility (clang, 16, false)	3m 1s
Generate report / bvt-report	16s
	1h 18m 58s

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