fix[venom]: liveness analysis in some loops

[harkal]

What I did

Fixed a small issue with the calculation of liveness in the case of variables in simple loops.

How I did it

Refactored the liveness calculation algorithm to an iterative version over the recursive one. Along side some additional refactoring to make the code cleaner and easier to follow.

How to verify it

I added the test_liveness_simple_loop.py that failed without the fix

Commit message

fixes a small issue with the calculation of liveness when variables are
consumed inside of loops by refactoring the liveness calculation
algorithm to an iterative version over the recursive one

additional QOL refactoring:
- simplify convert_ir_basicblock - rename it to ir_node_to_venom
- fix bb well-formedness for deploy ir
- don't do deploy IR detection; rely on caller in CompilerData to call for
  both deploy and runtime IR
- remove findIRnode, it's no longer needed
- rename _convert_ir_basicblock to _convert_ir_bb
- add _convert_ir_bb_list helper to handle arglists

Description for the changelog

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[codecov-commenter]

Codecov Report

Attention: 52 lines in your changes are missing coverage. Please review.

Comparison is base (81c6d8e) 84.18% compared to head (cc4c174) 84.86%.

Files	Patch %	Lines
vyper/venom/ir_node_to_venom.py	36.36%	40 Missing and 2 partials ⚠️
vyper/compiler/phases.py	0.00%	4 Missing ⚠️
vyper/venom/__init__.py	50.00%	2 Missing ⚠️
vyper/venom/analysis.py	85.71%	0 Missing and 2 partials ⚠️
vyper/venom/basicblock.py	0.00%	1 Missing ⚠️
vyper/venom/function.py	0.00%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3732      +/-   ##
==========================================
+ Coverage   84.18%   84.86%   +0.68%     
==========================================
  Files          92       92              
  Lines       13143    13128      -15     
  Branches     2928     2927       -1     
==========================================
+ Hits        11064    11141      +77     
+ Misses       1659     1525     -134     
- Partials      420      462      +42     

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