fix: reset Kint CSP state in worker mode

[memleakd]

This fixes stale Kint renderer state in worker mode.

Kint stores CSP nonces and rich renderer pre-render state in static properties. In normal PHP execution those statics are discarded after each request, but in worker mode they persist across requests. This can cause Debug Toolbar/Kint inline assets to use stale CSP nonces and trigger browser CSP violations.

This change resets Kint's request-specific renderer state from CodeIgniter::resetForWorkerMode() without reinitializing Kint or adding new public API.

• Refreshes Kint script/style CSP nonces per worker request
• Clears stale Kint nonces when CSP is disabled
• Restores RichRenderer::$needs_pre_render for the next request
• Adds regression coverage for worker reset behavior
• Adds a changelog entry

Fixes #10138

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value (without duplication)
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[mergeable]

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[michalsn]

Thank you for discovering, reporting, and fixing this. Truly the ideal situation.

Looks good to me.

Although for the 4.8 branch, we will need a small adjustment because CSP is lazy-loaded. I can take care of that later.

[paulbalandan]

Thank you, @memleakd