feat(bts): unit tests solidity bts

[sdpisreddevil]

Closes #598

Checklist:

• I have performed a self-review of my own code
• I have documented my code in accordance with the documentation guidelines
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• I have run the unit tests
• I only have one commit (if not, squash them into one commit).
• I have a descriptive commit message that adheres to the commit message guidelines

[codecov]

Codecov Report

Merging #599 (4c94bb0) into main (10d00dd) will increase coverage by 8.52%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##               main     #599      +/-   ##
============================================
+ Coverage     38.31%   46.84%   +8.52%     
  Complexity      700      700              
============================================
  Files           109       98      -11     
  Lines         10263     9338     -925     
  Branches        941      745     -196     
============================================
+ Hits           3932     4374     +442     
+ Misses         6007     4627    -1380     
- Partials        324      337      +13     

Impacted Files	Coverage Δ
solidity/bts/contracts/test/BMC.sol	54.16% <ø> (+54.16%)	⬆️
cmd/iconbridge/chain/bsc/client.go	62.87% <0.00%> (-1.52%)	⬇️
solidity/bts/contracts/libraries/DecodeBase64.sol
solidity/bts/contracts/test/NonRefundable.sol
solidity/bts/contracts/BTSCoreV1.sol
solidity/bts/contracts/libraries/EncodeBase64.sol
...lidity/bts/contracts/libraries/RLPDecodeStruct.sol
...lidity/bts/contracts/libraries/RLPEncodeStruct.sol
solidity/bts/contracts/BTSCoreV2.sol
solidity/bts/contracts/test/Holder.sol
... and 13 more

[izyak]

Remove the doc folder which has empty markdown file.
Remove empty files ocs/icon/bmc.md, docs/bsc/bmc.md.

[andrii-kl]

Remove the doc folder which has empty markdown file. Remove empty files ocs/icon/bmc.md, docs/bsc/bmc.md.

@sdpisreddevil

[andrii-kl]

Why we commented so many test cases in the next files, the one file was fully commented?
solidity/bts/test/integration/1-upgradeability-native-coin-bts.js
solidity/bts/test/integration/2-native-coin-bts.js