Implement BiRefNet and HAT Sharper models with background removal capabilities

- Added validation documentation for AI model tiers.
- Introduced `background.py` for background removal logic, including inference functions for alpha and foreground extraction.
- Created `onnx_birefnet.py` to handle BiRefNet model sessions and alpha inference.
- Developed tests for background models, ensuring proper dispatch and session reuse.
- Added tests for BiRefNet ONNX model to validate alpha output and error handling for invalid values.
- Implemented model export scripts for BiRefNet and HAT Sharper, ensuring proper weight compression and licensing.
- Created `deform_sampling.py` for deformable convolution operations used in BiRefNet.
- Added utility functions for compressing ONNX weights without altering graph arithmetic.
- Introduced a reference plane node for depth field adjustments in geometry processing.

tools/nodes/groups/image_depth_balloon.py

@@ -7,6 +7,7 @@ from ..common.nodes import (
     menu_switch, read_float_attribute, store_float_attribute, prepare_node_group,
 )
 from ..common.smoothing import expand_smooth
+from ..common.reference_plane import reference_plane_depth
 from ..common.cutout import _extrude_layers, _island_cleanup, _position_field, _profile_field, _remove_zero_thickness, _set_layer_z, _shade_output
 
 
@@ -29,35 +30,6 @@ def _set_geometry_z(group, geometry, z_value):
     return set_position.outputs["Geometry"]
 
 
-def _plane_depth(group, direction, reference_depth):
-    nodes = group.nodes
-    links = group.links
-    normal = nodes.new("ShaderNodeVectorMath")
-    normal.operation = "NORMALIZE"
-    links.new(direction, normal.inputs[0])
-    normal_components = nodes.new("ShaderNodeSeparateXYZ")
-    links.new(normal.outputs["Vector"], normal_components.inputs["Vector"])
-    position = nodes.new("GeometryNodeInputPosition")
-    position_components = nodes.new("ShaderNodeSeparateXYZ")
-    links.new(position.outputs["Position"], position_components.inputs["Vector"])
-    x_term = math_node(nodes, "MULTIPLY")
-    links.new(position_components.outputs["X"], x_term.inputs[0])
-    links.new(normal_components.outputs["X"], x_term.inputs[1])
-    y_term = math_node(nodes, "MULTIPLY")
-    links.new(position_components.outputs["Y"], y_term.inputs[0])
-    links.new(normal_components.outputs["Y"], y_term.inputs[1])
-    point_dot = math_node(nodes, "ADD")
-    links.new(x_term.outputs[0], point_dot.inputs[0])
-    links.new(y_term.outputs[0], point_dot.inputs[1])
-    divide = math_node(nodes, "DIVIDE")
-    links.new(point_dot.outputs[0], divide.inputs[0])
-    links.new(normal_components.outputs["Z"], divide.inputs[1])
-    plane = math_node(nodes, "ADD")
-    links.new(reference_depth, plane.inputs[0])
-    links.new(divide.outputs[0], plane.inputs[1])
-    return plane.outputs[0]
-
-
 def _build_depth_balloon(
     group,
     geometry,
@@ -78,7 +50,7 @@ def _build_depth_balloon(
     metric_depth = math_node(nodes, "MULTIPLY")
     links.new(separate_camera.outputs["Z"], metric_depth.inputs[0])
     links.new(uniform_scale, metric_depth.inputs[1])
-    plane_depth = _plane_depth(
+    plane_depth = reference_plane_depth(
         group,
         depth_direction,
         depth_reference,