fix[codegen]: fix abi_encode buffer size in external calls

[cyberthirst]

What I did

• fix Incorrect Buffer Size Passed to abi_encode() #4188

Commit Message

fix the buffer size passed to the abi encoder from the external call
argument packer. previously, the size was overestimated as it didn't
take into account pointer arithmetic performed on the buffer passed to
abi_encode.

this is a hygienic fix, no security implications were found for this
issue.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.80%. Comparing base (c0cf436) to head (385be9c).
Report is 52 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4202      +/-   ##
==========================================
- Coverage   91.32%   88.80%   -2.53%     
==========================================
  Files         109      109              
  Lines       15625    15627       +2     
  Branches     3442     3442              
==========================================
- Hits        14270    13878     -392     
- Misses        924     1240     +316     
- Partials      431      509      +78     

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