chore: rename vyper-ir to fang

[charles-cooper]

What I did

as title. also allow it to be run directly like python vyper/cli/vyper_ir.py.

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

Cute Animal Picture

[codecov-commenter]

Codecov Report

Merging #2936 (3b8f11a) into master (8eed257) will decrease coverage by 0.01%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #2936      +/-   ##
==========================================
- Coverage   88.32%   88.30%   -0.02%     
==========================================
  Files          97       97              
  Lines       10771    10773       +2     
  Branches     2565     2566       +1     
==========================================
  Hits         9513     9513              
- Misses        800      802       +2     
  Partials      458      458              

Impacted Files	Coverage Δ
vyper/cli/vyper_ir.py	0.00% <0.00%> (ø)

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