2879 extend staketable contract to override voting methods

[alysiahuggins]

Closes #2879

This PR:

• modifies StakeTable to integrate with OpenZeppelin's VotesUpgradeable for on-chain governance
• adds _getVotingUnits override to reflect voting power based on staking delegation
• adds validation to prevent invalid delegation scenarios (e.g., validator delegating to self, or delegating to different validators)
• updates delegate and undelegate logic to allow delegating all tokens or a specific amount, and properly handles partial and full undelegations

This PR does not:

• implement fuzz testing, marked as TODO
• override checkpoints and numCheckpoints logic, marked as TODO
• also need to get better at describing staking, delegating in the comments

Key places to review:

• contracts/src/StakeTable.sol: core changes to logic, inheritance
• contracts/test/StakeTable.t.sol: tests for voting behavior under VotesUpgradeable.
• _delegateStake and _undelegateStake internal functions
• the override of _getVotingUnits and delegate() to ensure compatibility with OpenZeppelin governance.

How to test this PR:

• forge test --match-contract StakeTableVotes