feat: store expansion pass

[charles-cooper]

What I did

sketch out store expansion pass

How I did it

How to verify it

Commit message

Commit message for the final, squashed PR. (Optional, but reviewers will appreciate it! Please see our commit message style guide for what we would ideally like to see in a commit message.)

Description for the changelog

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[codecov]

Codecov Report

Attention: Patch coverage is 95.16129% with 3 lines in your changes missing coverage. Please review.

Project coverage is 88.75%. Comparing base (3371956) to head (adbf01c).
Report is 6 commits behind head on master.

❗ Current head adbf01c differs from pull request most recent head 61ea577

Please upload reports for the commit 61ea577 to get more accurate results.

Files	Patch %	Lines
vyper/venom/passes/extract_literals.py	92.59%	1 Missing and 1 partial ⚠️
vyper/venom/passes/store_expansion.py	96.77%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4068      +/-   ##
==========================================
- Coverage   91.25%   88.75%   -2.50%     
==========================================
  Files         108      110       +2     
  Lines       15522    15582      +60     
  Branches     3410     3423      +13     
==========================================
- Hits        14164    13830     -334     
- Misses        926     1239     +313     
- Partials      432      513      +81     

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