Add crs and bin size metadata fields to VariableMetadata

Add crs, bin_inl, and bin_xl optional fields to support coordinate
reference system and bin size metadata for seismic data variables.

Made-with: Cursor

Author: keylgonz

src/mdio/builder/schemas/v1/variable.py

@@ -44,6 +44,21 @@ class VariableMetadata(CoordinateMetadata):
         description="Minimal summary statistics.",
     )
 
+    crs: str | None = Field(
+        default=None,
+        description="Coordinate Reference System as an EPSG code (e.g., 'EPSG:4326').",
+    )
+
+    bin_inl: float | None = Field(
+        default=None,
+        description="Inline bin size in grid units.",
+    )
+
+    bin_xl: float | None = Field(
+        default=None,
+        description="Crossline bin size in grid units.",
+    )
+
 
 class Coordinate(NamedArray):
     """A simple MDIO Coordinate array with metadata.

tests/unit/v1/test_dataset_builder_add_variable.py

@@ -178,6 +178,9 @@ def test_add_variable_full_parameters() -> None:
         attributes={"MGA": 51, "UnitSystem": "Imperial"},
         chunk_grid=RegularChunkGrid(configuration=RegularChunkShape(chunk_shape=(20,))),
         stats_v1=stats,
+        crs="EPSG:32610",
+        bin_inl=12.5,
+        bin_xl=25.0,
     )
     builder.add_variable(
         "ampl",
@@ -214,3 +217,6 @@ def test_add_variable_full_parameters() -> None:
     assert v.metadata.stats_v1.max == 10.84
     assert v.metadata.stats_v1.histogram.bin_centers == [1, 2]
     assert v.metadata.stats_v1.histogram.counts == [10, 15]
+    assert v.metadata.crs == "EPSG:32610"
+    assert v.metadata.bin_inl == 12.5
+    assert v.metadata.bin_xl == 25.0