Arm backend: mypy fixes (#8092)

Fix mypy warnings in arm_vela.py

In arm_vela.py, function vela_compile() there is a reuse of the
variable block_length that was of different type between uses and mypy
complained.

Change name of block_length that is used inside the loop to
block_length_bytes since its not a int.

Fix mypy warnings in arm_model_evaluator.py

Annotate a dict to fix mypy warning.

Author: perheld

backends/arm/arm_vela.py

@@ -96,13 +96,13 @@ def vela_compile(tosa_graph, args: List[str], shape_order=None):
                 block_name = block_name + b"\x00" * (16 - len(block_name))
 
                 # We need the acual unpadded block lengths for hw setup
-                block_length = struct.pack("<iiii", len(bin_blocks[key]), 0, 0, 0)  # type: ignore[assignment]
+                block_length_bytes = struct.pack("<iiii", len(bin_blocks[key]), 0, 0, 0)
 
                 # Pad block data to multiple of 16 bytes
                 block_data = bin_blocks[key]
                 block_data = block_data + b"\x00" * (15 - (len(block_data) - 1) % 16)
 
-                block = block_name + block_length + block_data  # type: ignore[operator]
+                block = block_name + block_length_bytes + block_data
                 blocks = blocks + block
 
         return blocks

backends/arm/operators/node_visitor.py

@@ -44,7 +44,7 @@ def define_node(
 
 
 # container for all node visitors
-_node_visitor_dicts = {  # type: ignore[var-annotated]
+_node_visitor_dicts: Dict[TosaSpecification, Dict] = {
     TosaSpecification.create_from_string("TOSA-0.80+BI"): {},
     TosaSpecification.create_from_string("TOSA-0.80+MI"): {},
 }

backends/arm/util/arm_model_evaluator.py

@@ -59,7 +59,7 @@ def __init__(
         if tosa_output_path:
             self.tosa_output_path = tosa_output_path
         else:
-            self.tosa_output_path = None  # type: ignore[assignment]
+            self.tosa_output_path = ""
 
     def get_model_error(self) -> defaultdict:
         """
@@ -104,7 +104,7 @@ def get_compression_ratio(self) -> float:
 
         return compression_ratio
 
-    def evaluate(self) -> dict[Any]:  # type: ignore[type-arg]
+    def evaluate(self) -> dict[str, Any]:
         model_error_dict = self.get_model_error()
 
         output_metrics = {"name": self.model_name, "metrics": dict(model_error_dict)}