Python bindings: expose boolean and comparison operators

In particular, expose comparison operators as Python operator overloads on
ValueHandles.  The comparison currently emits signed integer comparisons only,
which is compatible with the behavior of emitter-based EDSC interface.  This is
sub-optimal and must be reconsidered in the future.  Note that comparison
operators are not overloaded in the C++ declarative builder API precisely
because this avoids the premature decision on the signedness of comparisons.

Implement the declarative construction of boolean expressions using
ValueHandles by overloading the boolean operators in the `op` namespace to
differentiate between `operator!` for nullity check and for boolean negation.
The operands must be of i1 type.  Also expose boolean operations as Python
operator overloads on ValueHandles.

PiperOrigin-RevId: 238421615