🛡️ Sentinel: [HIGH] Fix XSS vulnerabilities in state event previews

[kevinaboos]

🚨 Severity: HIGH
💡 Vulnerability: User-controlled fields within AnyOtherStateEventContentChange (such as room aliases, room versions, custom guest access and history visibility rules, and tombstone replacement URIs) were being concatenated directly into HTML previews without being sanitized. This could allow an attacker to inject arbitrary HTML into the preview rendering of timeline events if a malicious payload was set.
🎯 Impact: Exploitation could lead to Cross-Site Scripting (XSS) allowing a malicious actor to inject code or break the UI layout when viewing compromised state events.
🔧 Fix: Wrapped the extraction logic for user-provided fields in text_preview_of_other_state with htmlize::escape_text when formatting as HTML. Used zero-allocation Cow::Borrowed when escaping is not needed.
✅ Verification: Ran cargo check and cargo test --lib to ensure the program compiles cleanly and all unit tests pass without regressions.

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PR created automatically by Jules for task 1905180717600848654 started by @kevinaboos

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