chore(benchmark): add app.fetch() overhead benchmark

[yusukebe]

These benchmark scripts enable measuring the performance of app.fetch(). This means it does not cover the HTTP layer and enables strict measurement of the application handler's speed.

compare.sh can run the benchmark multiple times to avoid inconsistency with order or conditions.

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

[github-actions]

HTTP Performance Benchmark

Framework	Runtime	Average	Ping	Query	Body
hono (origin/main)	bun	47,023.05	57,901.90	45,436.94	37,730.31
hono (current)	bun	45,014.01	54,079.68	43,707.56	37,254.78
Change		-4.27%	-6.60%	-3.81%	-1.26%

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.08%. Comparing base (fb9d7bf) to head (ff4f80d).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5117   +/-   ##
=======================================
  Coverage   79.08%   79.08%           
=======================================
  Files         154      154           
  Lines       10764    10764           
  Branches     2254     2254           
=======================================
  Hits         8513     8513           
  Misses       2251     2251           

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