bugfix: typosquatting fix top packages format

[sobregosodd]

Context:
Typosquatting relies on top_packages json files to identify if the scanned package resembles a known one.
There is a functionality that refreshes the file if is older than 30 days in the filesystem.
A recent contribution introduced an error that makes the program exists if the json file is refreshed.

This PR:

• Fixes the downloaded format error when file is refreshed.
• Refactors code so that the refresh logic is only in the parent's typosquatting class instead of replicated in every ecosystem
• Changes the refresh behaviour, the oldness of the json file is now tracked in the json file itself (downloaded_timestamp), since filesystem age is not a good fit: it's set when guarddog is installed or built, not when the list was collected

[ikretz]

lgtm