deps/dev: add basedpyright for type checking

pyproject.toml

@@ -19,7 +19,8 @@ capnpc-py = "capnp_stubgen.plugin:main"
 
 [dependency-groups]
 dev = [
-  "pytest>=8",
+    "pytest>=8",
+    "basedpyright>=1.39.9",
 ]
 
 [build-system]
@@ -34,3 +35,16 @@ testpaths = ["tests"]
 
 [tool.setuptools.packages.find]
 where = ["src"]
+
+[tool.basedpyright]
+typeCheckingMode = "recommended"
+allowedUntypedLibraries = ["pycapnp"]
+reportImportCycles = "hint"
+
+# Downgraded to hint for capnp to_dict() dynamic data patterns
+reportUnknownVariableType = "hint"
+reportUnknownArgumentType = "hint"
+reportUnknownMemberType = "hint"
+reportUnknownParameterType = "hint"
+reportAny = "hint"
+reportExplicitAny = "hint"