feat: add pseudolocalize options

[ThibaultJanBeyer]

Description

The current pseudolocalization doesn't allow for padding to catch UI bugs caused by longer languages.
Here is the related issue: #2582

Types of changes

The signature of the pseudoLocale can now look either like this:

// before
export default defineConfig({
  locales: ['en', 'pseudo'],
  sourceLocale: 'en',
  pseudoLocale: 'pseudo',
  catalogs: [],
})

or like this:

// after
export default defineConfig({
  locales: ['en', 'pseudo'],
  sourceLocale: 'en',
  pseudoLocale: { locale: 'pseudo', prepend: '⟦ ', append: ' ⟧', extend: 0.4 },
  catalogs: [],
})

• 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 #2582

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)
  (I'm not sure, added it to website/docs/ref/conf.md. Somewhere else to add?

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Project	Deployment	Actions	Updated (UTC)
js-lingui	Ready	Preview	Jun 26, 2026 10:35am

[timofei-iatsenko]

i suggest not export that from the package, but instead apply and normalize config in the makeConfig. So all consumers would receive normalized (expanded) option

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.75%. Comparing base (6bb8983) to head (a5215b9).
⚠️ Report is 354 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2583       +/-   ##
===========================================
+ Coverage   77.05%   89.75%   +12.69%     
===========================================
  Files          84      125       +41     
  Lines        2157     3698     +1541     
  Branches      555     1112      +557     
===========================================
+ Hits         1662     3319     +1657     
+ Misses        382      341       -41     
+ Partials      113       38       -75     

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