[Feature][BC break] Allow creating diffs from array and shift URL generation to DiffEntry

[IonBazan]

These changes are to make it easier to reuse this project as dependency as demonstrated in https://github.com/lyrixx/composer-diff. If you haven't checked it out yet, I strongly recommend you to do so - it's very useful if you don't have access to your PHP interpreter locally.

From user-perspective, there are no behavior changes except for json formatter. This refactoring is just opening up some classes to make it easier to integrate with this project.

• Shift UrlGenerator logic calls from Formatters to DiffEntry - this dramatically reduces complexity of each formatter and makes them more consistent. It also allows using DiffEntry objects in other applications.
• Allows generating the diff from pre-existing array and not just files - this actually could make it easier to test but also allows the web version to use a simpler API
• DiffEntry is now much more powerful - it allows to fetch all details like versions, licenses and URLs in a really simple way.
• BC break: DiffEntry now requires passing $urlGenerator before $direct (should be fine if you haven't provided the second argument.
• BC break: Using custom URL generators requires calling PackageDiff::setUrlGenerator() but the call is optional - it uses default GeneratorContainer out of the box.
• BC break: licenses key in json formatter is now an array instead of string|null @giggsey you might need to adjust your flows if you rely on this key

Note: All classes in this project are to be treated as internal as no BC promise is provided so far and they might change without prior notice. Backward compatibility is mostly provided for user-facing components like CLI arguments and formatters output.

As always, all PHP versions from 5.3 all the way to 8.5+ are supported and 100% code coverage is maintained.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (347c63c) to head (7692708).

Additional details and impacted files

@@             Coverage Diff             @@
##                main       #43   +/-   ##
===========================================
  Coverage     100.00%   100.00%           
- Complexity       241       242    +1     
===========================================
  Files             21        21           
  Lines            704       696    -8     
===========================================
- Hits             704       696    -8     

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