feat: saner accounting logic

[gomesalexandre]

See https://github.com/shapeshift/rFOX/pull/1#discussion_r1555557727

This PR:

• Ensures saner accounting, by making it so that calling requestWithdraw actually doesn't do any complex logic of "withdraw request resets the previous one under x condition, or replaces it under y condition" but instead does some simple accounting i.e decreases the staking balance and increases the unstaking balance.
• Introduces a new StakingInfo struct containing the staking balance, unstaking balance, and cooldown expiry timestamp, and a stakingInfo() view fn for it
• Removes cooldownInfo() since this data is now exposed by stakingInfo()
• balanceOf now behaves as a regular balanceOf i.e "for a given address, give me the amount of tokens I have in the smart contract, regardless of the ramifications of them being still staked and earning rewards, or in the process of being unstaked, with no rewards being earned"

[gomesalexandre]

Happy to merge and keep moving forward, but left some other comments around the run e address data type and verification

Ty @0xean ! Will merge, restack and tackle as part of the upmost PR in the stack i.e https://github.com/shapeshift/rFOX/pull/13