fix: stop file-based execution after snippet deactivation

[robertstaddon]

Fixes #561

Changes

• Flush the snippet object cache before get_snippet() in deactivate_snippet(), and set the snippet inactive before the file-based deactivate hook runs.
• Force $snippet->active = false in Snippet_Files::deactivate_snippet() so a stale cached object cannot be written into index.php as still active.
• Replace each type’s on-disk index with the currently active set when file-based files are rebuilt, instead of merging into leftover entries.

Verification

• Confirmed the same deactivate_snippet() order is still present on core-beta.
• Applied the same edits on a Code Snippets Pro 3.10.2 site with file-based execution enabled. After deactivating a global PHP snippet that printed a footer marker, the marker was gone on the front end and php/index.php recorded the snippet as inactive. Rebuilding the files did not mark it active again.

Made with Cursor

[ramiy]

Ideally, I would initially add a test that check file-based execution for deactivated snippets. The test should fail.

In a separate PR, which fixes the issue, the test should no longer fail.

[robertstaddon]

Thank you!