No need to scan a file if it was not changed

[sgarouachi]

Prevent performing a scan when the file was not changed, create a cache to track files last scan results

• path
• last scanned
• discoveries
• hash

if the file hash does not change, read discoveries from the cache otherwise force a scan
still be able to run a full scan using the vscode command (force mode),
prevent triggering a scan for a file when there's a scan in progress (locking)