Update multi-site redirect caching

[OscarBarrett]

Description

• Ensure a redirect applies to a site before returning it
• Delete redirects from cache if they do not apply to the site in the request
• Added warnings for fail cache deletions or redirects that were attempted but should not have been applied for a site
• Added unit tests

Running tests locally:

$ XDEBUG_MODE=coverage composer test
Codeception PHP Testing Framework v5.3.5 https://stand-with-ukraine.pp.ua

Unit Tests (5) ----------------------------------------------------------------------------------------------------
✔ BaseUnitTest: Plugin instance (0.01s)
✔ BaseUnitTest: Craft edition (0.00s)
✔ RedirectsServiceCacheTest: Save redirect to cache uses explicit site partition (0.01s)
✔ RedirectsServiceCacheTest: Find redirect match ignores cache entry for different site (0.01s)
✔ RetourUnitTest: Sanitize url (0.01s)
-------------------------------------------------------------------------------------------------------------------


Code Coverage Report:       
  2026-05-06 05:50:15       
                            
 Summary:                   
  Classes:  0.00% (0/6)     
  Methods:  4.92% (3/61)    
  Lines:   15.24% (181/1188)

nystudio107\retour\helpers\Text
  Methods:   0.00% ( 0/ 3)   Lines:  33.33% (  6/ 18)
nystudio107\retour\helpers\UrlHelper
  Methods:   0.00% ( 0/ 5)   Lines:  25.86% ( 15/ 58)
nystudio107\retour\services\Redirects
  Methods:  10.00% ( 3/30)   Lines:  22.50% (160/711)
Remote CodeCoverage reports are not printed to console

XML report generated in coverage.xml
Time: 00:15.267, Memory: 168.50 MB

OK (5 tests, 15 assertions)

Related issues

#357

[khalwat]

Very cool, will review