Add hakunapi-tiles-source-vectortile: Java MVT generator source

[jampukka]

Adds the community module that renders Mapbox Vector Tiles on the fly from feature collections.

• VectorTileGeneratorSource
  • The VectorTileSource registered as vectortile-generator: resolves a tile address to a ground bbox (TileContext) and hands it to the layer's generator
  • Generator is chosen by type id (vectortile.generator, or service-wide default.tiles.layers.vectortile.generator); tiles.vector=true auto-publishes every geometry collection through it
• VectorTileGenerator / VectorTileGeneratorProvider
  • ServiceLoader SPI for swappable generators; the provider fails on duplicate type ids. EmptyVectorTileGenerator (empty) produces a valid empty tile for routing and conformance checks
• JavaVectorTileGenerator
  • The in-JVM generator: reads geometry through NavigableHakunaGeometry, fuses the world-to-tile transform into one pass (geom.RingLoad), clips, snaps/simplifies and encodes straight into the layer encoder
  • Per-type writers (MvtPointGeometryWriter, MvtLineGeometryWriter, MvtPolygonGeometryWriter) over AbstractMvtGeometryWriter
• mvt package
  • MvtLayerEncoder encodes one layer back-to-front with key/value dedup; BackwardProtoBuf is the back-to-front chunked buffer; MvtTileWriter streams the tile out
• No new third-party dependencies