chore!: Remove manual serialization of Opcodes in favour of serde

[kevaundray]

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Description

Discussed internally: We originally wanted an encoding which could be implemented in other languages easier. I thought that having a manual encoding and then specifying this in some documentation would have been the best way for this. Even if this was the case, we have had two serialization bugs and the effort for folks to modify this code has become unproductive.

There are still solutions to the problem of having other languages implement a deserialization strategy, they can choose to use rmp/json for example, which is available in most languages. For now, we use rmp by default with the read and write methods.

Summary of changes

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Dependency additions / changes

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Test additions / changes

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Checklist

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt with default settings.
• I have linked this PR to the issue(s) that it resolves.
• I have reviewed the changes on GitHub, line by line.
• I have ensured all changes are covered in the description.

Additional context

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[kevaundray]

Closes #228

[vezenovm]

I think you can remove to_u16() and from_u16() in black box func file

[kevaundray]

I think you can remove to_u16() and from_u16() in black box func file

This was there prior to the manual serialization work so we probably want to check if this is being used in other places.

[vezenovm]

This was there prior to the manual serialization work so we probably want to check if this is being used in other places.

I see it only being used in the consistent_index test in black_box_functions.rs

[kevaundray]

This was there prior to the manual serialization work so we probably want to check if this is being used in other places.

I see it only being used in the consistent_index test in black_box_functions.rs

Checked Noir too and they are not being used, so I removed it