Arm backend: Fix get_quant_properties return type

The function `get_quant_properties` can return `None`, which was not
reflected in its return type annotation. This could cause type checker
warnings or incorrect assumptions about its return value.

Update the return type from `_OpQuantProperties` to
`_OpQuantProperties | None` to correctly represent the possible outputs.

Change-Id: I1f360ab1b9dcda119473f17a3eb46ffbaeba831c
Signed-off-by: Sebastian Larsson <[email protected]>

Author: Sebastian-Larsson

backends/arm/quantizer/quantization_annotator.py

@@ -245,7 +245,7 @@ def _match_pattern(
 
 def get_quant_properties(  # noqa: C901
     node: Node, gm: torch.fx.GraphModule, quantization_config
-) -> _OpQuantProperties:
+) -> _OpQuantProperties | None:
     input_act_qspec = quantization_config.get_input_act_qspec()
     weight_qspec = quantization_config.get_weight_qspec()
     output_act_qspec = quantization_config.get_output_act_qspec()
@@ -384,16 +384,16 @@ def any_or_hardtanh_min_zero(n: Node):
         quant_properties.quant_output = None
     elif node.target in _parent_shared_qspec:
         if not isinstance(node.args[0], Node):
-            return None  # type: ignore[return-value]
+            return None
 
         if not arm_quantizer_utils.is_output_annotated(node.args[0]):  # type: ignore[attr-defined]
-            return None  # type: ignore[return-value]
+            return None
 
         shared_qspec = SharedQuantizationSpec(node.args[0])
         quant_properties.quant_inputs = [_QuantProperty(0, shared_qspec)]  # type: ignore[arg-type]
         quant_properties.quant_output = _QuantProperty(0, shared_qspec)  # type: ignore[arg-type]
     else:
-        return None  # type: ignore[return-value]
+        return None
 
     # Don't check if operator.getitem is ok for quantization, it's always ok
     if node.target == operator.getitem:
@@ -402,7 +402,7 @@ def any_or_hardtanh_min_zero(n: Node):
     # Check that each inputs/outputs can be quantized properly with the
     # provided quantization properties.
     if not _is_ok_for_quantization(node, quant_properties, gm):
-        return None  # type: ignore[return-value]
+        return None
 
     return quant_properties