perf(aws-lambda): optimize header parsing to reduce micro-allocations

[fcarvajalbrown]

Description

This PR optimizes the getHeaders method in the AWS Lambda adapter. By switching from Object.entries() to a for...in loop with a safety check, we avoid the overhead of creating intermediate arrays for every request.
In high-throughput serverless environments, reducing these "micro-allocations" significantly lowers Garbage Collection (GC) pressure and minimizes latency jitter.

Performance Details

benchmark avg (min … max) p75 / p99

---

Current (Object.entries) 1.26 µs/iter 1.20 µs / 2.30 µs
Optimized (for...in) 851.85 ns/iter 860.13 ns / 954.57 ns

Summary:
Optimized (for...in) is 1.48x faster than Current (Object.entries)

Testing

[x] Benchmark Validation: Verified with mitata (results above).

[x] Functional Testing: Ran the full Hono test suite.

[x] Runtime Verification: Verified that globalThis.Headers is correctly populated.

[x] Logic Safety: Added hasOwnProperty check to ensure we only process own properties of the event.headers object.

[usualoma]

Hi @fcarvajalbrown
Thank you for creating the pull request.

For future pull requests, please include a description following this template:
https://github.com/honojs/hono/blob/main/.github/pull_request_template.md

Regarding this pull request, I believe it is a reasonable small improvement.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.48%. Comparing base (df97e5f) to head (40d8dce).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4762   +/-   ##
=======================================
  Coverage   91.48%   91.48%           
=======================================
  Files         177      177           
  Lines       11551    11555    +4     
  Branches     3353     3352    -1     
=======================================
+ Hits        10567    10571    +4     
  Misses        983      983           
  Partials        1        1           

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[yusukebe]

Checking hasOwnProperty is really necessary? I think the eventHandlers is a plain object ({}), so it's unnecessary. What do you think of it?

[BarryThePenguin]

for...in also enumerates properties in the prototype chain. Object.keys() doesn't, so you can skip hasOwnProperty

[yusukebe]

@fcarvajalbrown Can you handle this?

[fcarvajalbrown]

yes sorry i will, been busy with work on the weekends but now i am available! cheers!