fix(adapter/aws-lambda): APIGWProxyResult should contain either of headers or multiValueHeaders, not both

[exoego]

Closes #3870

• APIGWProxyResult now contains headers or multiValueHeaders mutually-exclusively.
• handle is tweaked so the response type can be inferred from the request event type.

The author should do the following, if applicable

• Add tests
• Run tests
• bun run format:fix && bun run lint:fix to format the code
• Add TSDoc/JSDoc to document the code

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.77%. Comparing base (093d3fd) to head (ed5fe62).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3883      +/-   ##
==========================================
- Coverage   90.78%   90.77%   -0.01%     
==========================================
  Files         162      162              
  Lines       10263    10259       -4     
  Branches     2908     2900       -8     
==========================================
- Hits         9317     9313       -4     
  Misses        945      945              
  Partials        1        1              

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