Add option to track heap memory usage of memos

[ibraheemdev]

#[salsa::tracked(heap_size)] will require the return type of a tracked function to implement the get_size2::GetSize trait, and include the heap size in the new memory usage APIs. I'm not sure get-size2 is the best crate to use, but it seems relatively comprehensive, and integrating it into ty was relatively simple with its derive macros. Note that it's not actually a dependency of salsa, it's just called by the generated proc-macro code.

[netlify]

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[codspeed-hq]

CodSpeed Performance Report

Merging #925 will not alter performance

_{Comparing ibraheemdev:ibraheem/memory-usage-dump (5f33cd3) with master (8d14c02)}

Summary

✅ 12 untouched benchmarks

[MichaReiser]

Thanks this is great. I've only one recommendation on how we could possibly remove the get_size dependency entirely (in tests and in the generated macro)