Along with the changes to rescale op attributes, commit 7208649 dropped
the builtin casts between signed and signless types. However, explicitly
unsigned types are still legal input and output values from the TOSA IR
perspective.
The change adds back the casts when the unsigned<->signless semantics
are explicit in the underlying tensor types. This prevents the
conversion routine from trying to generate illegal `arith` casts that
are constrained to signless types. Whether the `arith` casts themselves
are signed or unsigned should still depend on the rescale's `*_unsigned`
attribute values.
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Signed-off-by: Artem Gindinson <gindinson@roofline.ai>
d03f30fb52