Update ProviderConfig to Use Uint8Array Instead of Buffer for coinbase

[schaable]

This is not a high-priority change, but in the ideal scenario, the coinbase field of the ProviderConfig interface would accept a Uint8Array instead of a Buffer.

The motivation is to move away from Node.js-specific types, such as Buffer, to facilitate supporting other runtimes in the future. Currently, Hardhat is casting from Uint8Array to Buffer when passing the coinbase to EDR.

Work should be done in the feat/multichain branch.

[IftequarIffu]

Hey @schaable, should the work be done on feat/multichain branch?

[Wodann]

Yes, ideally it would be. I updated the issue description to reflect this.