Add API: `make_proxy_observed` #18

Job	Run time
Run BVT with MSVC / bvt-msvc	10m 58s
Run BVT with GCC / bvt-gcc	8m 13s
Run BVT with NVHPC / bvt-nvhpc	16m 20s
Run BVT with Clang / bvt-clang	9m 53s
Run BVT for compatibility / bvt-compatibility (clang, 20, true)	3m 3s
Run BVT with AppleClang / bvt-appleclang	6m 22s
Run BVT for compatibility / bvt-compatibility (gcc, 14, true)	1m 52s
Run BVT for compatibility / bvt-compatibility (clang, 19, false)	3m 39s
Run BVT with Intel oneAPI / bvt-oneapi	10m 11s
Run BVT for compatibility / bvt-compatibility (clang, 17, false)	3m 5s
Run BVT for compatibility / bvt-compatibility (clang, 18, false)	3m 2s
Build mkdocs / bvt-mkdocs	20s
Run BVT for compatibility / bvt-compatibility (clang, 16, false)	2m 36s
Run BVT for compatibility / bvt-compatibility (gcc, 13, false)	1m 37s
Generate report / bvt-report	28s
	1h 21m 39s

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