feat: implement signed shift

[charles-cooper]

What I did

add shift for int256

How I did it

How to verify it

Commit message

add shift for signed integers. use SAR instruction for the right shift,
and disable SAR emulation for pre-constantinople arches since the
emulation is not simple.

- fix bad argtypes
- wrap evm_pow to prevent optimizer from hanging on large inputs

Description for the changelog

implement shift for signed integers

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[codecov-commenter]

Codecov Report

Merging #2964 (d1800b6) into master (c3e43d7) will decrease coverage by 0.02%.
The diff coverage is 94.11%.

❗ Current head d1800b6 differs from pull request most recent head 5a185ca. Consider uploading reports for the commit 5a185ca to get more accurate results

@@            Coverage Diff             @@
##           master    #2964      +/-   ##
==========================================
- Coverage   88.16%   88.13%   -0.03%     
==========================================
  Files          97       97              
  Lines       10820    10810      -10     
  Branches     2569     2564       -5     
==========================================
- Hits         9539     9527      -12     
- Misses        823      825       +2     
  Partials      458      458              

Impacted Files	Coverage Δ
vyper/codegen/core.py	84.90% <0.00%> (ø)
vyper/builtin_functions/functions.py	90.86% <100.00%> (-0.11%)	⬇️
vyper/ir/optimizer.py	95.03% <100.00%> (ø)
vyper/utils.py	90.00% <100.00%> (+0.16%)	⬆️
vyper/codegen/ir_node.py	91.69% <0.00%> (-0.70%)	⬇️

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