fix: add casts and add suppression to make pyright happy

This commit fixes some problems found by `pyright`:
* In the DuckDB test, a `bytes` parameter is wrongly annotated as `str`
  in the stub files of that Python module. We silence that false
  positive with a suppression.
* In the test for converting MLIR ops to plans, we use some op-specific
  members on an object whose most narrow known type is `MlirOperation`,
  so the commit adds a `cast` to make the `typing` information more
  precise.

test/python/dialects/substrait/e2e_duckdb.py

@@ -49,7 +49,7 @@ def testNamedTable():
   pb_plan = ss.to_binpb(plan.operation).encode()
 
   # Execute in duckdb and print result.
-  query_result = con.from_substrait(proto=pb_plan)
+  query_result = con.from_substrait(proto=pb_plan)  # type: ignore
 
   print(query_result.to_arrow_table())
   # CHECK-NEXT:          pyarrow.Table

test/python/dialects/substrait/translate.py

@@ -9,6 +9,7 @@
 # RUN: %PYTHON %s 2>&1 | FileCheck %s
 
 import json
+from typing import cast
 
 from substrait_mlir.dialects import substrait as ss, arith
 from substrait_mlir.ir import Context, Location
@@ -42,7 +43,7 @@ def testJsonFormat():
   print(json_plan)
   # CHECK: {"version":{"minorNumber":42,"patchNumber":1}}
 
-  plan_op = plan_module.body.operations[0]
+  plan_op = cast(ss.PlanOp, plan_module.body.operations[0])
   print(plan_op.to_json())
   # CHECK: {"version":{"minorNumber":42,"patchNumber":1}}
 
@@ -68,7 +69,7 @@ def testTextPB():
   # CHECK-NEXT:   minor_number: 42
   # CHECK-NEXT:   patch_number: 1
 
-  plan_op = plan_module.body.operations[0]
+  plan_op = cast(ss.PlanOp, plan_module.body.operations[0])
   print(plan_op.to_textpb())
   # CHECK:      version {
 
@@ -86,7 +87,7 @@ def testBinPB():
   print(bin_plan)
   # CHECK: 2
 
-  plan_op = plan_module.body.operations[0]
+  plan_op = cast(ss.PlanOp, plan_module.body.operations[0])
   print(plan_op.to_binpb())
   # CHECK: 2