Add API: `make_proxy_observed` #20

Job	Run time
Run BVT with MSVC / bvt-msvc	11m 13s
Run BVT with AppleClang / bvt-appleclang	7m 46s
Run BVT with NVHPC / bvt-nvhpc	18m 30s
Build mkdocs / bvt-mkdocs	22s
Run BVT with Clang / bvt-clang	9m 50s
Run BVT with GCC / bvt-gcc	7m 57s
Run BVT with Intel oneAPI / bvt-oneapi	10m 10s
Run BVT for compatibility / bvt-compatibility (clang, 19, false)	3m 8s
Run BVT for compatibility / bvt-compatibility (clang, 16, false)	2m 59s
Run BVT for compatibility / bvt-compatibility (gcc, 13, false)	1m 30s
Run BVT for compatibility / bvt-compatibility (clang, 17, false)	3m 7s
Run BVT for compatibility / bvt-compatibility (gcc, 14, true)	1m 47s
Run BVT for compatibility / bvt-compatibility (clang, 18, false)	3m 1s
Run BVT for compatibility / bvt-compatibility (clang, 20, true)	3m 5s
Generate report / bvt-report	19s
	1h 24m 44s

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