Claude review: gpu: nova-core: gsp: simplify sequencer opcode parsing

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

This replaces the roundabout pattern of creating a byte slice from the union field and then parsing it via `FromBytes` with a direct read of the union field. The safety comments are preserved and correct - the opcode is checked before accessing the union, so the union field access is valid.

> -        let payload_bytes = unsafe {
> -            core::slice::from_raw_parts(
> -                core::ptr::addr_of!(self.0.payload.regWrite).cast::<u8>(),
> -                core::mem::size_of::<RegWritePayload>(),
> -            )
> -        };
> -        Ok(*RegWritePayload::from_bytes(payload_bytes).ok_or(EINVAL)?)
> +        Ok(RegWritePayload(unsafe { self.0.payload.regWrite }))

Since the payload types are `#[repr(transparent)]` wrappers around the binding types, constructing them directly from the union field is sound. The `from_bytes` call could never fail anyway (the types implement `FromBytes`), so removing it doesn't change behavior - it just removes unnecessary indirection. The same pattern is repeated for all five payload types.

No issues found.

---
Generated by Claude Code Patch Reviewer