Add QubitizationWalkOperator examples for chemistry

[tanujkhattar]

Most of the bloqs in chemistry/ package (eg: THC) have examples for SELECT and PREPARE but there are no examples for constructing a walk operator out of these SELECT and PREPARE lcu oracles. In many cases, it's non trivial to plug them together and there are also bugs (eg: discovered in https://github.com/quantumlib/Qualtran/pull/732/files#r1520492441). Another related issue is #549

This issue is to go through all the chemistry factorizations and add bloq examples for constructing QubitizationWalkOperator that can then be tested (eg: used for constructing flame graphs to visualize resource costs etc.)

[fdmalone]

My strategy here is to add the examples and then go back and write a notebook comparing costs. Will require a QROAM bloq too.