[Mosaic TPU] Improve error message for unsupported scalar AddIOp
The arith::addi operation fails with a confusing message when adding integer scalars with unsupported types (currently only 32 bits are supported). Improve that by introducing a new check in the canonicalization pass to verify the element type. If the type is unsupported, it now emits a clear and helpful error message.
Additionally, a new test, `test_scalar_integer_addition`, is added to verify the correct behavior.
PiperOrigin-RevId: 805013869