perf[venom]: improve CSE elimination speed

[charles-cooper]

What I did

How I did it

How to verify it

Commit message

in the CSE elimination pass, avoid `O(n*k)` (where `n` == number of
instructions, and `k` == number of available expressions) copies
by replacing the dict with a HAMT. HAMT is an immutable dict with
`O(1)` copy (copy by reference), and `O(log N)` insert/delete/update
operations, each returning a fresh reference to a new HAMT.

we pull in the external package `immutables`, which is stable, shares
maintainership with CPython, and seems mature (receives bugfixes every
now and again, but mostly not adding new features). we pull in the
external library since HAMTs should be generally useful for the types
of lattice operations we do, and we can probably use them to optimize
other passes as well.

this commit also adds the use of `lru_cache` for some `Flag` operations
(which are bizarrely a perf hotspot)

Description for the changelog

Cute Animal Picture

[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	immutables@​0.21

View full report

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.81%. Comparing base (2fa2dcc) to head (d6897e7).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4607      +/-   ##
==========================================
+ Coverage   92.79%   92.81%   +0.01%     
==========================================
  Files         131      131              
  Lines       18845    18858      +13     
  Branches     3274     3273       -1     
==========================================
+ Hits        17488    17503      +15     
+ Misses        928      927       -1     
+ Partials      429      428       -1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[HodanPlodky]

Why did you not use with as in the add method?

[charles-cooper]

good question, i think i just didn't like the level of nesting 😂

i think both versions do more or less the same thing though

[cyberthirst]

approved without review. with @charles-cooper we analyzed the risks of introducing the new dependency a few weeks ago and reached consensus it should be safe