Move gravity direction system to Anthology

Gravity API, mixins, projectile compat, inverted effect, gravity sync and
/gravity now live in the Anthology library. Antarchy registers the Underside
region, antiwater, stale-inversion cleanup and portal gun camera roll through
GravityHooks, and depends on the local Anthology jar in anthology_jars/.

fabric-1.21.1/src/main/resources/fabric.mod.json

@@ -33,6 +33,7 @@
   ],
   "depends": {
     "antos": ">=1.2.1",
+    "anthology": ">=1.0.0",
     "fabricloader": ">=${fabric_loader_version}",
     "minecraft": "~${minecraft_version}",
     "java": ">=21",