Ensure validate_state() is called after update_state() to enforce state validity and reduce redundant validation

[sanity]

To prevent buggy or malicious contract behavior from propagating invalid states across the network, we should enforce a design where validate_state() is always called after update_state(). This will ensure that the state remains valid after a delta is applied, without relying on redundant validation inside the update_state() function itself. We should remove the validate_delta() function (if present) and explicitly discourage performing state validation within update_state(), as validate_state() will handle this post-update validation.

[gogo2464]

OH nice can I be assigned to this please?