Improve state size validation

[Mrtenz]

This PR contains a couple changes related to JSON size validation in the snap_manageState and snap_setState methods:

• The maximum size was reduced from 100 MB to 64 MB. This is to because window.postMessage breaks when sending payloads that are too large. This is technically a breaking change, but I'm not sure if it should be considered as one, given that the execution environment would throw regardless, if the new state is too big?
• snap_setState now properly validates the size of the new state, like snap_manageState does.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.76%. Comparing base (687b582) to head (8829423).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3025   +/-   ##
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  Coverage   94.76%   94.76%           
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  Files         499      499           
  Lines       10906    10906           
  Branches     1674     1672    -2     
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  Hits        10335    10335           
  Misses        571      571           

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