feat: assoc method completion #1936

Job	Run time
Check	3m 9s
Test mdbook	4m 2s
Test Rust (ubuntu-22.04)	3m 40s
Doctest Rust (ubuntu-22.04)	1m 12s
Test C++ Runtime (ubuntu-22.04)	3m 39s
Test Rust (windows-latest)	12m 29s
Doctest Rust (windows-latest)	4m 43s
Test C++ Runtime (windows-latest)	8m 35s
Test Rust (macOS-latest)	3m 30s
Check Style	1m 29s
Doctest Rust (macOS-latest)	1m 16s
Test C++ Runtime (macOS-latest)	2m 29s
	50m 13s

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