[Misc] Centralize and remove redundant casts to validation code

[amirebrahimi]

If you search for int( you'll find casts throughout a lot of the codebase. This might be left-over from before _params_validation() was added. The task is to remove these redundant casts and add a few assertions/additional tests as needed.

[anonymousr007]

Hi @amirebrahimi, I am Rishabh from India, recently contributed in Cirq and Pennylane and I want to make a PR for this issue, can you please elaborate little bit more?