kaiax/gov: add crits and fix kaia_getParams

[ian0371]

Proposed changes

Add Crit on unexpected error; it may be better to panic than to continue with invalid value.

For backward compatibility, fix the return type of kaia_getParams from int to string for reward.mintingamount and reward.minimumstake.

See #189 (comment)

Types of changes

• Bugfix
• New feature or enhancement
• Others

Checklist

• I have read the CONTRIBUTING GUIDELINES doc
• I have read the CLA and signed by comment I have read the CLA Document and I hereby sign the CLA in first time contribute
• Lint and unit tests pass locally with my changes ($ make test)
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in downstream modules

[hyeonLewis]

Testing results and all issues resolved.

> kaia.getParams("latest")
{ 
  ...
  reward.minimumstake: "5000000",
  reward.mintingamount: "9600000000000000000",
  ...
}

> governance.getParams(112492799)
{
  governance.deriveshaimpl: 2,
  ...
}

> kaia.getChainConfig(112492799)
{
  ...
  deriveShaImpl: 2,
  ...
}