Clarify or Utilize `round` Parameter in `PendingStake` Method

[rickstaa]

In the PendingStake method of the BondingManager, the round parameter is currently unused:

https://github.com/livepeer/protocol/blob/e8b6243c48d9db33852310d2aefedd5b1c77b8b6/contracts/bonding/BondingManager.sol#L935

To improve clarity and reduce potential confusion for integrators and developers, I propose one of the following actions:

1. Update the method description and documentation to explicitly state that the round parameter is currently unused, and clarify its intended purpose (if any future usage is planned).

2. Upgrade the protocol to make use of the round parameter, if there is an intended use case (e.g., allowing querying of stake at a specific round).

This change will help avoid misinterpretation and make the API more intuitive and self-explanatory for future development and integrations.