Track durations should be configurable

Currently all music discs have a track length of five minutes. As far as I know, as of 1.19.,3, the only effect this has on the vanilla game is that it dictates how long Allays will dance for.

However, the SBM-Jukebox mod has evidently implemented the Bedrock behavior of locking music discs while playing (See: https://github.com/StrikerRockers-Mods/SBM-Jukebox-fabric/issues/2). Thus, this value may actually matter for some players (like myself) when making redstone-powered playlists.

Thus:

[ ] The default duration of any track should be read in from the foxnap.yaml nested entry track_length -> default (if such a key isn't set, the default track length should be 30 seconds, which is hopefully shorter than anything someone would want to play, giving folks the chance to manage their jukebox unloading with hopper clocks and whatnot)
[ ] Tracks 1-7 should have default duration matching their actual length, but this should be overridable via config using the nested key: track_length -> track_n (where "n" is 1, 2, 3, etc.)

To drive the point home, the default foxnap.yaml should look like:

n_discs: 7
track_length:
    default: 60
    track_1: 4m39s
    track_2: 6m46s
    track_3: 1m48s
    track_4: 1m42s
    track_5: 3m43s
    track_6: 2m19s
    track_7: 1m19s

Note that each entry should accept either integer number of a simple m+s syntax--let's try not to worry too much about diabolical inputs--just assume that "s" is optional and that the formula of xmys is "x * 60 + y"

This is the end-state solution to the surprise that was strikerrocker actually implementing my suggestion--#31 is the version of the story that needs to be handled immediately.

Updating the resource pack generator to grab and set durations is out of scope (see #32).

OpenBagTwo / FoxNap

Track durations should be configurable #30