feat: establish formal raster particle source chain

particle-fixtures/nodata/metadata.json

@@ -0,0 +1,15 @@
+{
+  "schema": "maplibre-particle-fixture/v1",
+  "fixtureId": "nodata",
+  "fieldType": "WIND",
+  "displayDomain": "GLOBAL",
+  "dataVersion": 1,
+  "timeIndex": 0,
+  "timestamp": null,
+  "bounds": {"west": -180.0, "south": -85.0, "east": 180.0, "north": 85.0},
+  "crs": "EPSG:4326",
+  "grid": {"width": 16, "height": 16, "registration": "node", "origin": "north-west", "rowOrder": "north-to-south", "columnOrder": "west-to-east"},
+  "vector": {"uPositive": "east", "vPositive": "north", "unit": "m/s", "layout": "interleaved-uv", "encoding": "float32-le", "noData": -9999.0, "file": "field.f32"},
+  "mask": {"mode": "none"},
+  "integrity": {"fieldByteLength": 2048, "fieldSha256": "5756a6ac403a435ff001ff7261160de718c4a2964434ba7b9be2bfe74f071ff0"}
+}