fix: [Cache] Double prefix for increment in FileHandler

[il-coder]

Description
When using some default prefix in cache config with FileHandler being used, the increment function would save the updated result with the key having the prefix twice. To fix it, instead of passing the already prefixed key, now it is passing the non-prefixed key to the save function and save function itself appends the prefix when calling validateKey.

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

[kenjis]

Thank you! LGTM!

and all other handlers also have this bug.

[il-coder]

Thank you! LGTM!

Welcome

and all other handlers also have this bug.

No, other handlers call their extension/library implementation functions. I was working with redis extension and it worked fine. But with file handler, I was facing the issue.