fix: add error handling for corrupted cache files in FileHandler

[michalsn]

Description
This PR fixes the FileHandler::getItem() method to gracefully manage corrupted or malformed cache files that cannot be read or unserialized.

• unserialize() is now wrapped in a try/catch block, since it may throw a Throwable that the @ operator cannot suppress
• file_get_contents() and unlink() are prefixed with @ to suppress warnings, as these functions only emit warnings and do not throw exceptions

Fixes#9573

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[whiskey-coder]

can you add error log. when content is false

[michalsn]

Since this is a caching library, corrupted or unreadable files are expected edge cases, and logging every occurrence could easily flood logs in high-traffic environments. Silent failure is acceptable here, as cache misses are non-critical by design.

[michalsn]

Thanks everyone!