signTypedData: `uint` and `int` fields should be forbidden

Right now, signTypedData will accept `uint` and `int`, but EIP 712 states that only integer types with their size are allowed.

Trying to use these should error, telling users that `uint256` and `int256` should be used instead when encountering these types.

Start at the signTypedData entry point and trace validation of integer field types. Confirm that bare uint and int are rejected with guidance to use uint256 and int256, then verify the behavior with the relevant existing tests.

Written by the indexing model from the issue text.