Add API: `make_proxy_observed` #23

Job	Run time
Run BVT with MSVC / bvt-msvc	11m 5s
Run BVT with Clang / bvt-clang	46s
Run BVT with AppleClang / bvt-appleclang	8m 31s
Run BVT with NVHPC / bvt-nvhpc	13m 14s
Run BVT with Intel oneAPI / bvt-oneapi	10m 5s
Build mkdocs / bvt-mkdocs	19s
Run BVT with GCC / bvt-gcc	8m 27s
Run BVT for compatibility / bvt-compatibility (clang, 16, false)	2m 49s
Run BVT for compatibility / bvt-compatibility (clang, 17, false)	3m 4s
Run BVT for compatibility / bvt-compatibility (clang, 20, true)	3m 6s
Run BVT for compatibility / bvt-compatibility (clang, 18, false)	2m 59s
Run BVT for compatibility / bvt-compatibility (clang, 19, false)	2m 58s
Run BVT for compatibility / bvt-compatibility (gcc, 13, false)	1m 31s
Run BVT for compatibility / bvt-compatibility (gcc, 14, true)	1m 49s
Generate report	0s
	1h 10m 43s

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