[ty] Add environment variable to dump Salsa memory usage stats

[ibraheemdev]

Summary

Setting TY_MEMORY_REPORT=full will generate and print a memory usage report to the CLI after a ty check run:

=======SALSA STRUCTS=======
`Definition`                                       metadata=7.24MB   fields=17.38MB  count=181062
`Expression`                                       metadata=4.45MB   fields=5.94MB   count=92804
`member_lookup_with_policy_::interned_arguments`   metadata=1.97MB   fields=2.25MB   count=35176
...
=======SALSA QUERIES=======
`File -> ty_python_semantic::semantic_index::SemanticIndex`
    metadata=11.46MB  fields=88.86MB  count=1638
`Definition -> ty_python_semantic::types::infer::TypeInference`
    metadata=24.52MB  fields=86.68MB  count=146018
`File -> ruff_db::parsed::ParsedModule`
    metadata=0.12MB   fields=69.06MB  count=1642
...
=======SALSA SUMMARY=======
TOTAL MEMORY USAGE: 577.61MB
    struct metadata = 29.00MB
    struct fields = 35.68MB
    memo metadata = 103.87MB
    memo fields = 409.06MB

Eventually, we should integrate these numbers into CI in some form. The one limitation currently is that heap allocations in salsa structs (e.g. interned values) are not tracked, but memoized values should have full coverage. We may also want a peak memory usage counter (that accounts for non-salsa memory), but that is relatively simple to profile manually (e.g. time -v ty check) and would require a compile-time option to avoid runtime overhead.

Depends on salsa-rs/salsa#925.

[github-actions]

mypy_primer results

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[github-actions]

ruff-ecosystem results

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[MichaReiser]

This is great

I've a few smaller nits. The only downside of the design is that it's very easy to forget the heap_size attribute on a salsa query which will result in under counting. That makes me wonder if we should change the design in salsa so that the stack and heap_size is reported separately for each query (we can show a total as well) and the heap_size would be Unknown if the heap_size attribute isn't set. This would make it more appearant where heap_size attributes are missing (compared to, ah, this query doesn't allocate much)

[MichaReiser]

It would be nice if:

• We would print a condenced memory report when running with -vv
• We would print the full memory report when running with -vvv

You can get the verbosity from args.verbosity.

I would probably skip the environment variable for now. If we don't, make sure to add it here https://github.com/astral-sh/ty/blob/main/docs/reference/env.md

[ibraheemdev]

I think having to run -vvv is a little difficult because of the amount of tracing logs you have to wait for :) I kept the environment variable but added short and full options. We might eventually have to add an option for mypy primer that keeps the diff less sensitive to minor changes.