feat[venom]: add function inliner

[harkal]

What I did

How I did it

How to verify it

Commit message

This commit adds a function inliner to the Venom backend, including:

- A basic heuristic to determine when inlining is beneficial
  (placeholder for future sophisticated analysis)
- new machinery for global (inter-function) passes over Venom IR to
  perform inlining
- A new function call graph analysis to support inlining
- Removal of the variable equivalence analysis (now provided directly by
  DFG analysis)

misc/refactor:
- add new `all2` utility function
- add dfs preorder traversal to CFG
- add ensure_well_formed util to IRBasicBlock
- machinery for IRParameter (may be useful in the future)
- add `copy()` machinery for venom data structures (may be useful in the
  future)

Description for the changelog

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[codecov]

Codecov Report

Attention: Patch coverage is 87.67773% with 52 lines in your changes missing coverage. Please review.

Project coverage is 91.99%. Comparing base (cd31867) to head (3b15a33).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
vyper/venom/basicblock.py	67.85%	18 Missing ⚠️
vyper/venom/function.py	56.66%	13 Missing ⚠️
vyper/venom/analysis/cfg.py	57.14%	9 Missing ⚠️
vyper/venom/context.py	70.00%	6 Missing ⚠️
vyper/venom/passes/function_inliner.py	97.85%	1 Missing and 2 partials ⚠️
vyper/venom/venom_to_assembly.py	71.42%	2 Missing ⚠️
vyper/venom/passes/base_pass.py	88.88%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4478      +/-   ##
==========================================
- Coverage   92.12%   91.99%   -0.13%     
==========================================
  Files         119      120       +1     
  Lines       16962    17292     +330     
  Branches     2872     2930      +58     
==========================================
+ Hits        15626    15908     +282     
- Misses        919      963      +44     
- Partials      417      421       +4     

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[cyberthirst]

just checking legacy part