feat[venom]: improve liveness computation

[charles-cooper]

What I did

move dfs order calculation from domtree to cfg analysis.

remove unnecessary calculation of domtree in sccp

remove redundant IRFunction.compute_reachability

change cfg_out order

refactor shared phi fixup code

How I did it

How to verify it

Commit message

feat[venom]: improve liveness computation

traversing in reverse topsort order improves stack scheduling slightly

this commit also adds a topsort method to CFGAnalysis, and speeds it up
by only checking the terminator instruction instead of iterating over
all the instructions in every basic block.

additional refactors:
- move dfs order calculation from domtree to cfg analysis.
- remove unnecessary calculation of domtree in sccp
- remove redundant IRFunction.compute_reachability
- change cfg_out order
- refactor shared phi fixup code
- remove useless `__eq__()` and `__hash__()` for IRBasicBlock

Description for the changelog

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[codecov]

Codecov Report

Attention: Patch coverage is 29.78723% with 33 lines in your changes missing coverage. Please review.

Project coverage is 46.13%. Comparing base (063f190) to head (78da77c).

Files with missing lines	Patch %	Lines
vyper/venom/analysis/cfg.py	24.00%	19 Missing ⚠️
vyper/venom/function.py	16.66%	5 Missing ⚠️
vyper/venom/analysis/dominators.py	62.50%	3 Missing ⚠️
vyper/venom/passes/simplify_cfg.py	0.00%	2 Missing ⚠️
vyper/venom/venom_to_assembly.py	33.33%	2 Missing ⚠️
vyper/venom/analysis/liveness.py	0.00%	1 Missing ⚠️
vyper/venom/passes/sccp/sccp.py	50.00%	1 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (063f190) and HEAD (78da77c). Click for more details.

HEAD has 97 uploads less than BASE

Flag	BASE (063f190)	HEAD (78da77c)
	98	1

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #4330       +/-   ##
===========================================
- Coverage   91.30%   46.13%   -45.18%     
===========================================
  Files         112      112               
  Lines       15921    15916        -5     
  Branches     2691     2684        -7     
===========================================
- Hits        14537     7343     -7194     
- Misses        949     8018     +7069     
- Partials      435      555      +120     

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[charles-cooper]

hmm, this creates a regression in branch_storm.vy