fix(factory): correct the type of factory.createMiddleware()

[yusukebe]

Fixes #3847

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]

Bundle size check

	main (3fba7a5)	#3849 (0bf2bf7)	+/-
Bundle Size (B)	18,771B	18,771B	0B
Bundle Size (KB)	18.33K	18.33K	0K

Compiler Diagnostics

	main (3fba7a5)	#3849 (0bf2bf7)	+/-
Files	257	257	0
Lines	115,045	115,045	0
Identifiers	112,920	112,920	0
Symbols	301,426	301,426	0
Types	213,590	213,590	0
Instantiations	3,089,848	3,089,848	0
Memory used	445,523K	444,527K	-996K
I/O read	0.03s	0.02s	-0.01s
I/O write	0s	0s	0s
Parse time	0.69s	0.8s	0.11s
Bind time	0.29s	0.36s	0.07s
Check time	5.44s	5.41s	-0.03s
Emit time	0s	0s	0s
Total time	6.42s	6.57s	0.15s

---

Reported by octocov

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.32%. Comparing base (3fba7a5) to head (dbfe247).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3849   +/-   ##
=======================================
  Coverage   91.31%   91.32%           
=======================================
  Files         161      161           
  Lines       10240    10242    +2     
  Branches     2926     2902   -24     
=======================================
+ Hits         9351     9353    +2     
  Misses        888      888           
  Partials        1        1           

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