Add missing py.typed markers

[angrybayblade]

Proposed changes

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Fixes

If it fixes a bug or resolves a feature request, be sure to link to that issue.

Types of changes

What types of changes does your code introduce to agents-aea?
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• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

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• I have read the CONTRIBUTING doc
• I am making a pull request against the develop branch (left side). Also you should start your branch off our develop.
• Lint and unit tests pass locally with my changes and CI passes too
• I have added tests that prove my fix is effective or that my feature works
• I have checked that code coverage does not decrease.
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in downstream modules

[codecov-commenter]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (2be89a7) 91.99% compared to head (792ea85) 91.99%.
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #677      +/-   ##
==========================================
- Coverage   91.99%   91.99%   -0.01%     
==========================================
  Files         371      371              
  Lines       29539    29545       +6     
==========================================
+ Hits        27175    27179       +4     
- Misses       2364     2366       +2     

Flag	Coverage Δ
unittests	91.99% <ø> (-0.01%)	⬇️

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see 2 files with indirect coverage changes

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[solarw]

LGTM