[MLIR][LoopPipelining] Improve schedule verifier, so it checks also operands...

[MLIR][LoopPipelining] Improve schedule verifier, so it checks also operands of nested operations (#88450)

`verifySchedule` was not looking at the operands of nested operations,
which caused incorrect schedule to be allowed in some cases, potentially
leading to crash during expansion.
There is also minor fix in `cloneAndUpdateOperands` in the pipeline
expander that prevents double visit of the cloned op. This one has no
functional impact, so no test for it.