Update SIMD-406

[LucasSte]

This PR amends the SIMD with the feature gate key and removes the error type from the detailed design section. During the implementation, we noticed we should not specify the error type in the SIMD (see anza-xyz/agave#10223 (comment))

[simd-bot]

Hello LucasSte! Welcome to the SIMD process. By opening this PR you are affirming that your SIMD has been thoroughly discussed and vetted in the SIMD discussion section. The SIMD PR section should only be used to submit a final technical specification for review. If your design / idea still needs discussion, please close this PR and create a new discussion here.

This PR requires the following approvals before it can be merged:

• At least one approval from a Anza team member: t-nelson, sakridge, or bw-solana
• At least one approval from an Firedancer team member: ptaffet-jump, topointon-jump, 0x0ece, lidatong, or ripatel-fd

Once all requirements are met, you can merge this PR by commenting /merge.

[simd-bot]

Thanks, topointon-jump!

⚠️ Status: Cannot merge yet

• Missing approval from: Anza (t-nelson, sakridge, or bw-solana)

[LucasSte]

@t-nelson or @bw-solana any chance you can have a look here?

[simd-bot]

✅ All approvals received! @LucasSte, you can now merge this by commenting /merge.

✅ Status: Ready to merge

[LucasSte]

/merge

[simd-bot]

✅ Merge successful! LucasSte's PR has been merged.