[Custom VM] Improve and test instruction printer

[turbolent]

Description

• Use a bytes.Reader to avoid manual index calculations
• Return helpful errors
• Add tests

Eventually we can maybe generate the decoding and printing (as well as encoding) from a specification (e.g. Go code), similar to how it was done for the WebAssembly instructions in https://github.com/onflow/cadence/pull/3705/files#diff-82ca63eac37e62fe45b1499cde54ac1e090fd495ba7ef9716d03708d656daa8dL484

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• Targeted PR against master branch
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work
• Code follows the standards mentioned here
• Updated relevant documentation
• Re-reviewed Files changed in the Github PR explorer
• Added appropriate labels

[SupunS]

Nice!