fix: ♻️ Fix mypy issues

pyproject.toml

@@ -114,15 +114,15 @@ report.exclude_also = [
 [tool.mypy]
 mypy_path = "$MYPY_CONFIG_FILE_DIR/src,$MYPY_CONFIG_FILE_DIR/stubs"
 files = ["src", "tests"]
-python_version = "3.8"
+python_version = "3.9"
 strict = true
 enable_error_code = ["ignore-without-code", "redundant-expr", "truthy-bool"]
 warn_unreachable = true
 explicit_package_bases = true
 pretty = true
 
 [[tool.mypy.overrides]]
-module = ["types-Pillow", "jsonschema", "tsplib95.*", "ipywidgets.*", "IPython.*", "qiskit.*", "qiskit_algorithms.*", "matplotlib.*", "networkx.*", "mqt.ddsim.*", "joblib.*", "qiskit_optimization.*", "docplex.*", "typing_extensions.*"]
+module = ["types-Pillow", "jsonschema", "tsplib95.*", "ipywidgets.*", "IPython.*", "qiskit.*", "qiskit_algorithms.*", "matplotlib.*", "networkx.*", "mqt.ddsim.*", "joblib.*", "qiskit_optimization.*", "docplex.*", "typing_extensions.*", "numpy.*"]
 ignore_missing_imports = true
 
 [tool.ruff]

src/mqt/qubomaker/graph.py

@@ -2,7 +2,7 @@
 
 from __future__ import annotations
 
-from typing import TYPE_CHECKING, Tuple, Union
+from typing import TYPE_CHECKING, Tuple, Union, cast
 
 import networkx as nx
 import numpy as np
@@ -162,7 +162,7 @@ def __eq__(self, value: object) -> bool:
         """
         if not isinstance(value, Graph):
             return False
-        return np.array_equal(self.adjacency_matrix, value.adjacency_matrix)
+        return cast(bool, np.array_equal(self.adjacency_matrix, value.adjacency_matrix))
 
     def __hash__(self) -> int:
         """Returns the hash of the graph.

src/mqt/qubomaker/pathfinder/cost_functions.py

@@ -1284,7 +1284,7 @@ def get_variable_function(p: Any, v: Any, i: Any, _n: int = 0) -> sp.Expr:
     @override
     def get_formula_domain_wall(self, graph: Graph, settings: pathfinder.PathFindingQUBOGeneratorSettings) -> sp.Expr:
         general = self.get_formula_general(graph, settings, FormulaHelpers.get_encoding_variable_domain_wall)
-        enforce_domain_wall_penalty = (
+        enforce_domain_wall_penalty: sp.Expr = (
             2 * settings.max_path_length * np.max(graph.adjacency_matrix) + graph.n_vertices**2
         )
         # This ensures that the domain wall condition (x_i = 0 -> x_{i+1} = 0) is not broken to achieve better cost in other cost functions.

tests/resources/graph/graph

@@ -2,4 +2,4 @@
 0. 0. 0. 3. 0.
 0. 0. 0. 0. 2.
 0. 0. 0. 0. 5.
-1. 0. 0. 0. 0.
+1. 0. 0. 0. 0.