[DCME] Dynamic Contextual Music Engine

v1.0.3:
- Structure tags now work. The `structures` condition accepts "#namespace:tag" exactly like `biomes` already did, so one context can cover every mineshaft or every village instead of listing each mod's variant. The example datapack shows how to define your own structure tag.
- Fixed structure detection reading a structure's PIECES instead of its outline. Inside a Nether fortress the corridors counted but the courtyards and the gaps between rooms did not, so the music started and stopped as you walked through it.
- Fixed underground structures never being detected. The answer was cached per chunk COLUMN with no height, so once you had walked over the ground above a stronghold, "no structure" was cached for that whole column, for every player, and written to disk. Detection is now cached and re-run per 16 block section. The cache file has a new name (dcme_structures_v2.json); the old one is ignored and can be deleted.
- Fixed overlapping structures being resolved in registry order, which is arbitrary. The smallest structure now wins: it is the more specific answer, and it is stable.
- Fixed music playing at the SQUARE of your Music slider. At 50% the mod played at 25%, at 30% it played at 9%. The slider is now applied once.
- Fixed `dimension` and `structures` requiring the full namespace while the documentation showed the short form. `"dimension": "overworld"` was compared, character for character, against `minecraft:overworld`, so it never matched and said nothing. Biome conditions never had the problem, which is what made this one so hard to see. Both forms now work everywhere.
- Dying now resets the music the same way leaving a world does. The track that was playing when you died used to come back a second later, over the death screen, and carry on unchanged after you respawned. The death screen is now silent unless a pack provides a context for it, and respawning starts from a clean slate.
- Fixed the music carrying over into the next world. Going through a Nether portal, the Overworld track came back for about four seconds before the Nether track took over, and leaving a world started a track that the loading screen then cut off. Loading a world, leaving one and stepping through a portal now all reset the music cleanly: silence during the load, then the new world's music from a clean slate.
- Fixed the world-change check only looking at the DIMENSION, and only while a world was loaded, so leaving to the title screen was never detected at all.
- Fixed the startup log line reporting v1.0.0 whatever the actual version was. It now reads the real one, which matters when a log is the only thing you have to go on.
- A `screen` condition no longer cancels every other condition in the same context.
- Mistakes in a music context are now reported at load, with the file and the field named, instead of being dropped in silence: an unknown field (`biome` instead of `biomes`, for instance), a sound that no resource pack declares, and two contexts sharing one id. Contexts are also logged at INFO rather than DEBUG, so a pack that fails to load is visible at the default log level.
- Removed a pointless attempt to add resource pack sounds to the game's sound registry, which always failed and logged a misleading message. Sounds are resolved by identifier through the resource packs and never needed it.
- Drop in replacement: no config change, and the only save data touched is the structure cache described above.