Instruction Impl Type Inconsistency: Builder vs Unmarshal

[lukestoltenberg]

When unmarshalling a transaction from []byte it creates a pointer to the instruction's BaseVariant.Impl but when creating a token.Instruction using a builder like token.NewMintToCheckedInstructionBuilder() the BaseVariant.Impl is a value.

For example, token.NewMintToCheckedInstructionBuilder(), the .Build() sets the BaseVariant.Impl to the receiver value of inst MintToChecked

solana-go/programs/token/MintToChecked.go

Line 135 in a5e17d6

Impl: inst,

When using UnmarshalBin of a []byte, it sets the BaseVariant.Impl to a pointer, https://github.com/gagliardetto/binary/blob/79f49c5de0e11369897085d761a7e27cbd8eab15/variant.go#L320.

To fix this, I propose changing the instructions' .Build() to take a pointer receiver

func (inst *MintToChecked) Build() *Instruction