feat: add staking sdk

[voliva]

Some initial version, the api might change but so far it supports:

• Validator rewards
  • Validator info (commision, blocked, self stake, etc.)
  • Validator points + reward
  • nominator share
• Nominator rewards (expensive operations)
  • total and by validator
  • active validators
• Abstraction over balance into "total, locked, untouchable, spendable"
  • Maybe this should be another sdk? It's deeply related though
• Current nominating status
  • current bond
  • max bond
  • nomination eligibility
  • validator list
• Current pool membership status
  • current bond
  • pending rewards

[josepot]

Let's get this in!