docs: add performance optimization docs

[timofei-iatsenko]

Description

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Examples update

Fixes # (issue)

Checklist

• I have read the CONTRIBUTING and CODE_OF_CONDUCT docs
• I have added tests that prove my fix is effective or that my feature works
• I have added the necessary documentation (if appropriate)

[vercel]

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Name	Status	Preview	Updated (UTC)
js-lingui	✅ Ready (Inspect)	Visit Preview	Jul 28, 2025 8:10am

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.82%. Comparing base (6bb8983) to head (3928004).
⚠️ Report is 203 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2296      +/-   ##
==========================================
- Coverage   77.05%   76.82%   -0.24%     
==========================================
  Files          84       89       +5     
  Lines        2157     2498     +341     
  Branches      555      650      +95     
==========================================
+ Hits         1662     1919     +257     
- Misses        382      463      +81     
- Partials      113      116       +3     

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[vonovak]

or metro loader :)