refactor(ux): ensure that all known and knowable type errors raise `UnsupportedBackendType` instead of letting code pass through to the backend

[cpcloud]

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Right now we're letting types that we know (and can know) are invalid for a given backend. Unsigned integers are a good example of this.

We should ensure that these types never make it through, and perhaps more importantly all raise the same type of exception (ibis.common.exceptions.UnsupportedBackendType).