Disable snap on schematic gizmos

Schematic dimensions float in billboarded viewport space; their labels
carry the value, not the bar length. Snapping the dragged tip to scene
vertices produces nonsensical value jumps when the mouse crosses
unrelated meshes. Add an opt-out flag on the parametric gizmo group
base and override it on the schematic base — every schematic subclass
inherits no-snap behaviour, and in-place parametric gizmos (door,
window, wall, stair, roof, mep) keep the existing Ctrl-toggleable
snap because the default stays True.

GizmoDimension.invoke also forces tool_settings.use_snap = False for
schematic gizmos so the header magnet visibly switches off for the
drag's duration. The existing exit path restores the user's previous
setting on release.

Generated with the assistance of an AI coding tool.

src/bonsai/test/bim/module/drawing/test_gizmos.py

@@ -24,7 +24,11 @@ from types import SimpleNamespace
 import bpy
 import pytest
 
-from bonsai.bim.module.drawing.gizmos import DimensionGizmoConfig
+from bonsai.bim.module.drawing.gizmos import (
+    BaseParametricGizmoGroup,
+    BaseSchematicGizmoGroup,
+    DimensionGizmoConfig,
+)
 
 pytestmark = pytest.mark.drawing
 
@@ -52,3 +56,19 @@ def test_text_formatter_receives_props_and_value():
     config = DimensionGizmoConfig(attr_name="length", axis=(1, 0, 0), text_formatter=formatter)
     props = SimpleNamespace(label="L")
     assert config.text_formatter(props, 3.14) == "L=3.14"
+
+
+def test_parametric_base_enables_dimension_snap_by_default():
+    """In-place parametric gizmos align to real-world geometry, so dragging
+    must respect the global snap toggle (Ctrl-flip during drag) — same
+    contract every door / window / wall / stair / roof / mep dimension
+    has shipped with."""
+    assert BaseParametricGizmoGroup.snap_enabled_on_dimensions is True
+
+
+def test_schematic_base_disables_dimension_snap():
+    """Schematic dimensions float in viewport space; snapping the dragged
+    tip to scene vertices would produce spurious value jumps as the
+    mouse crosses unrelated geometry. The opt-out lives on the base so
+    every schematic subclass inherits it without per-class wiring."""
+    assert BaseSchematicGizmoGroup.snap_enabled_on_dimensions is False