Refactor: Extract the CountsDuration table logic into PlaylistStatsDAO

[cr7pt0gr4ph7]

SetlogFeature and PlaylistFeature (as well as BasePlaylistFeature) contain nearly identical code for creating a summary table of the track number and total duration of all playlists (both history playlists and normal playlists).

This PR unifies the code into a single PlaylistStatsDAO class, which has the added advantage of moving DB-layer code from the *Feature classes to a more appropriate location.

[ronso0]

Thank you for this PR!

Please note that there is already #4846 which also does a playlist backend refactoring.
I'd recommend to first check that PR and wait how we proceed with that before investing more time here.

[cr7pt0gr4ph7]

@ronso0: Thanks for the heads up! I am not especially partial to the code in this PR, it was a byproduct of understanding the playlist duration calculation logic while working on #13183 (which, in the end, was implemented in a wholly different way instead), and none of my other code depends on it.

So it's your call whether to merge this PR, or close it and wait for #4846 to finish - I am fine either way.

[cr7pt0gr4ph7]

It seems that #4846 was last updated in 2022, so I don't know whether to expect any progress on that.

My new PR #13183 calculates the total track time of the Auto DJ playlist (like #4846) but also takes intro/outro cues, transition times etc. fully into account by reusing the calculation logic that is used for performing the actual transitions,
so if merged, it would fully supersede #4846.

This PR is independent of that and is just a "nice to have" from a code quality perspective, so I'll leave it open for now. Feel free to close it in the future if it isn't needed anymore.

[ninomp]

Hi! Author of #4846 here. I'm currently struggling to find time to finish #4846, so feel free to go ahead with your work. When your PR gets merged, I'll close mine.

Also, If you are interested, I can review your PR(s) and give you my comments/ideas.