Add mcmc validator as transform

[JerryChen97]

Context:
As we have already implemented the _validate_mcmc_options helper to directly check mcmc options in execution config constructor, it is also important to have it actually added to the preprocess pipeline since with the decoupling between shots and device the only scenario when a device can get and validate the shots information will be the preprocess.
Given that, we would like to add the validator as a transform as well as keeping the original helper, before we entirely remove shots from Device on the PennyLane side (which should take a very long time).

Description of the Change:

Benefits:

Possible Drawbacks:

Related GitHub Issues:
[sc-103749]

[github-actions]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.69%. Comparing base (483c4d6) to head (4274977).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1234      +/-   ##
==========================================
+ Coverage   93.77%   94.69%   +0.91%     
==========================================
  Files         183      180       -3     
  Lines       30380    29307    -1073     
==========================================
- Hits        28490    27751     -739     
+ Misses       1890     1556     -334     

Flag	Coverage Δ
unit_tests	94.69% <100.00%> (+0.91%)	⬆️

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