test(lambda-edge): expand handler unit tests for createRequest, createResult, and env bindings

[rokasta12]

Summary

Expands unit test coverage for the Lambda@Edge handler from 5 tests to 33 (28 new). All new tests target untested code paths in handler.ts.

New coverage by area

isContentTypeBinary — 9 additional MIME types via it.each (csv, html+charset, xml variants, octet-stream, pdf, audio, video)

createBody — 4 new tests:

• PUT/DELETE/PATCH methods (non-GET/HEAD with body)
• Non-base64 (text) encoding
• Undefined requestBody
• Empty data string

createRequest (tested indirectly via handle) — 6 new tests:

• Host fallback to distributionDomainName when host header is absent
• Querystring appended to URL
• No trailing ? when querystring is empty
• CloudFront headers converted to Request headers
• No body for GET requests
• Base64 body decoding for POST requests

createResult (tested indirectly via handle) — 6 new tests:

• Status returned as string (CloudFront requirement)
• Non-200 status codes
• No bodyEncoding for text content
• bodyEncoding: 'base64' for binary content
• Response headers in CloudFront format
• 404 for unmatched routes

env bindings — 4 new tests:

• Event, config, request passed as env bindings
• Callback invocation
• No-throw when callback is not provided (optional chaining)
• Context passed as env binding

Coverage

Metric	Before	After
Statements	—	100%
Branches	—	96.66%
Functions	—	100%
Lines	—	100%

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.50%. Comparing base (2de30d7) to head (24a6f64).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4747      +/-   ##
==========================================
+ Coverage   91.48%   91.50%   +0.01%     
==========================================
  Files         177      177              
  Lines       11556    11556              
  Branches     3357     3359       +2     
==========================================
+ Hits        10572    10574       +2     
+ Misses        983      981       -2     
  Partials        1        1              

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