test: add simulation tests

[jaybxyz]

Description

This PR is contiunation of #83 that include simulation tests for both public and private plans.

closes: #64 #88

Actions

• add simulation tests for private plans (store decoders, randomized genesis and params, random weighted operations)
• add simulation tests for public plans (random proposal contents)
• add verification for duplicate plan name for private plans Add public and private plan creation #11

Further improvements

We need to come up with better ways to simulate public plan proposals. Currently, only basic logics are written.

And after genesis functionality with F1 logic is implemented, we plan to add below simulations

• add simulation test for running runsim to test import and export simulation
• add simulation test for running runsim to test simulation after import

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• Review Codecov Report in the comment section below once CI passes

[codecov]

Codecov Report

Merging #98 (f6222e3) into master (566057d) will increase coverage by 9.26%.
The diff coverage is 83.19%.

@@            Coverage Diff             @@
##           master      #98      +/-   ##
==========================================
+ Coverage   55.38%   64.64%   +9.26%     
==========================================
  Files          23       24       +1     
  Lines        1728     2062     +334     
==========================================
+ Hits          957     1333     +376     
+ Misses        662      598      -64     
- Partials      109      131      +22     

Impacted Files	Coverage Δ
x/farming/keeper/genesis.go	76.31% <ø> (ø)
x/farming/keeper/proposal_handler.go	36.84% <0.00%> (-0.57%)	⬇️
x/farming/types/codec.go	0.00% <ø> (-4.77%)	⬇️
x/farming/types/genesis.go	49.12% <0.00%> (-2.67%)	⬇️
x/farming/types/proposal.go	3.61% <0.00%> (+0.04%)	⬆️
x/farming/module.go	53.84% <14.28%> (-1.90%)	⬇️
x/farming/simulation/proposals.go	80.67% <80.67%> (ø)
x/farming/types/plan.go	37.34% <81.81%> (+6.72%)	⬆️
x/farming/keeper/staking.go	90.47% <84.61%> (-0.23%)	⬇️
x/farming/simulation/operations.go	92.12% <89.63%> (+92.12%)	⬆️
... and 5 more

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[jaybxyz]

Running runsim to test import/export simulation returns panic panic: expected PlanI, got <nil>.
This issue is related to #90. I will need to get back on this since there is more imminent issue to take care of.

[jaybxyz]

LGTM on simulation part. As you have stated offline, let's tackle this with other PR(s) since this PR is becoming huge.