fix[venom]: fix branch eliminator cases in sccp

[charles-cooper]

What I did

How I did it

How to verify it

Commit message

in sccp, when the operand of `jnz`, `djmp` or `assert` is already an
`IRLiteral` (this is most easily seen by disabling the IRnode branch
eliminator), the compiler will panic. this commit fixes the bug, and
refactor some commonly used code into helper functions.

Description for the changelog

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[harkal]

djmp is also "vulnerable" to passing a literal.

I think a better solution would be to never arrive here with literals in conditions. This will allow the algorithm to remain pure. A better place might be the remove_unreachable_blocks pass.

[charles-cooper]

how about literals inside of assertions?

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 96.96970% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 89.91%. Comparing base (93147be) to head (e39076a).

❗ Current head e39076a differs from pull request most recent head b02e098. Consider uploading reports for the commit b02e098 to get more accurate results

Files	Patch %	Lines
vyper/venom/passes/sccp/sccp.py	96.29%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4003      +/-   ##
==========================================
- Coverage   90.78%   89.91%   -0.87%     
==========================================
  Files         105      103       -2     
  Lines       15248    14915     -333     
  Branches     3362     3303      -59     
==========================================
- Hits        13843    13411     -432     
- Misses        966     1053      +87     
- Partials      439      451      +12     

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[charles-cooper]

i'm going to revert the changes to exp eval and the CI pipelines in order to keep this PR more "pure". will open those in a separate PR