Create processor in useEffect in MarkdownHooks

[remcohaszing]

Initial checklist

• I read the support docs
• I read the contributing guide
• I agree to follow the code of conduct
• I searched issues and discussions and couldn’t find anything or linked relevant results below
• I made sure the docs are up to date
• I included tests (or that’s not needed)

Description of changes

In MarkdownHooks we don’t need to create the processor for every render. We only need it inside the effect.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (2245c64) to head (4f8d5d1).
Report is 47 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##              main      #908    +/-   ##
==========================================
  Coverage   100.00%   100.00%            
==========================================
  Files            3         3            
  Lines         1354      1743   +389     
  Branches       113       123    +10     
==========================================
+ Hits          1354      1743   +389     

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[JounQin]

LGTM. Would it improve perf and resolve https://github.com/orgs/rehypejs/discussions/194?

[remcohaszing]

Not necessarily, but it does give me an idea. I need to fiddle a bit.

[remcohaszing]

I’m closing this in favor of #909

[wooorm]

please apply labels when closing, thanks!