enhancement: add find_many

[lostman]

Description

Closes #1467.

This PR adds the find_many() function to the Entity trait, which is like find(), except that it fetches multiple results.

Testing steps

CI tests should pass. This PR adds basic find_many tests to the existing find test.

Changelog

• Add find_many to the Entity trait.
• Rename QueryFragment to OrderedFilter. This way we have Filter and OrderedFilter, which easier to understand.
• Clean up some implementation details.

[ra0x3]

@lostman

• Left feedback regarding the usage of limit in your find_many implementation
• Will review again once that's fixed (since I think fixing that will shift some logic around)

[ra0x3]

Thanks @lostman