Problem: can't support prevrando opcode

[mmsqe]

Closes: #XXX

Description

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[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 61.54%. Comparing base (d874df7) to head (6a1c8c4).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #499      +/-   ##
===========================================
- Coverage    61.55%   61.54%   -0.01%     
===========================================
  Files          128      128              
  Lines         9496     9500       +4     
===========================================
+ Hits          5845     5847       +2     
- Misses        3111     3112       +1     
- Partials       540      541       +1     

Files	Coverage Δ
x/evm/keeper/config.go	91.17% <75.00%> (-2.58%)	⬇️

[mmsqe]

seems block time might differ between abci and grpc call

[yihuang]

Applications already mix a bunch of different factors to emulate randomness, I don't think we should emulate it, and the emulation won't be secure , until we have a real random oracle