chore: Bytecode is buffer not string

[spalladino]

After deserialization, bytecode should be represented internally as a buffer, not as a b64 string. We actually had several bugs where we were deserializing bytecode as hex instead of b64, which just silently returns an empty buffer because javascript. This PR removes all conversions back and forth between buffer and b64, and just deserializes in the loadContractArtifact function that handles conversion of all noir artifacts.

[spalladino]

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• feat: Capture broadcasted functions in node #5353
• chore: Bytecode is buffer not string #5351 👈
• docs(yellow-paper): Update function broadcasting functions #5350
• feat: Capture broadcasted unconstrained functions in node #5349
• feat: Capture broadcasted private fns in node #5318
• master

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[spalladino]

Closing in favor of merging everything in one go in #5353