Change projection_pushdown default to False

Functions must now explicitly opt-in to projection pushdown support by
setting `projection_pushdown = True` in their Meta class. This is safer
as a function incorrectly claiming projection support could lead to
incorrect results.

- Changed default from True to False in ResolvedMetadata
- Added projection_pushdown = True to ProjectedDataFunction (the only
  example function that actually implements projection optimization)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: rustyconover

vgi/examples/table.py

@@ -464,6 +464,7 @@ class Meta:
         description = "Generates data with 4 columns, supporting projection pushdown"
         categories = ["generator", "utility"]
         max_workers = 1
+        projection_pushdown = True
         examples = [
             FunctionExample(
                 sql="SELECT * FROM projected_data(10)",

vgi/metadata.py

@@ -322,7 +322,7 @@ class ResolvedMetadata:
     required_settings: list[str] = field(default_factory=list)
 
     # Table function specific
-    projection_pushdown: bool = True
+    projection_pushdown: bool = False
     filter_pushdown: bool = False
     preserves_order: OrderPreservation = OrderPreservation.PRESERVES_ORDER
     max_workers: int | None = None
@@ -368,7 +368,7 @@ def from_dict(d: dict[str, Any]) -> ResolvedMetadata:
             stability=FunctionStability[d.get("stability", "CONSISTENT")],
             null_handling=NullHandling[d.get("null_handling", "DEFAULT")],
             required_settings=d.get("required_settings", []),
-            projection_pushdown=d.get("projection_pushdown", True),
+            projection_pushdown=d.get("projection_pushdown", False),
             filter_pushdown=d.get("filter_pushdown", False),
             preserves_order=OrderPreservation[
                 d.get("preserves_order", "PRESERVES_ORDER")
@@ -790,7 +790,7 @@ class Meta:
         stability=attrs.get("stability", FunctionStability.CONSISTENT),
         null_handling=attrs.get("null_handling", NullHandling.DEFAULT),
         required_settings=attrs.get("required_settings", []),
-        projection_pushdown=attrs.get("projection_pushdown", True),
+        projection_pushdown=attrs.get("projection_pushdown", False),
         filter_pushdown=attrs.get("filter_pushdown", False),
         preserves_order=attrs.get("preserves_order", OrderPreservation.PRESERVES_ORDER),
         max_workers=attrs.get("max_workers"),