Use UInt8Array instead of a Buffer for coinbase in ProviderConfig

[IftequarIffu]

This PR fixes #746

[changeset-bot]

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Latest commit: 6f5c847

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[Wodann]

There are no changes on the Rust side to change the data size which would invalidate code generation of the index.d.ts and potentially introduce UB.

The investigation is meant to investigate a refactir on the Rust side