refactor: optimisation around stoptimes

- moved stoptime related functionality into new core:data:stoptime module
  - will feature all the different realtime stoptime sources to be
      integrated later
- create proper database schema for future migrations
- deduplicate trips into stoppingpatterns, since many trips share the
  exact same stopping pattern
  - stoptimes are now linked to stoppingpatterns instead
  - stoppingpattern ids are generated from a hash composed of all stoptimes
- stoptimes now use deltas for arrival time to save space

core/data/build.gradle.kts

@@ -27,6 +27,7 @@ kotlin {
     sourceSets {
         commonMain.dependencies {
             implementation(projects.core)
+            api(projects.core.data.stoptime)
         }
     }
 }