feat(types/buffer): skip copying in to_bytes when NonContiguous contains a single Bytes

[ever0de]

Which issue does this PR close?

Closes #5385

Rationale for this change

The Buffer::to_bytes method currently performs unnecessary copying when the buffer is NonContiguous but contains only a single Bytes. This results in reduced performance due to redundant data duplication. By optimizing to_bytes to return the single Bytes directly without copying, we can improve the efficiency of buffer operations.

What changes are included in this PR?

• Optimized the Buffer::to_bytes method to return the single Bytes directly when NonContiguous contains only one Bytes, avoiding unnecessary copying.

Are there any user-facing changes?

No user-facing changes. This optimization improves internal performance without altering the public API or behavior visible to users.

[Xuanwo]

Thank you @ever0de for optimizing this!

[ever0de]

Would it be better to perform an upstream rebase and update the commit messages as well? (perf -> feat)

[Xuanwo]

Would it be better to perform an upstream rebase and update the commit messages as well? (perf -> feat)

That's fine, we will squash all the commits. Thank you anyway!