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GH-34242: [C++][Parquet] Optimize comment and move for shared_ptr in parquet schema (#34243)



### Rationale for this change

This patch fix some comments, and remove some copying for shared_ptr, using reference or `std::move` instead.

### What changes are included in this PR?

Some comment and shared_ptr usage fix

### Are these changes tested?

No

### Are there any user-facing changes?

No

* Closes: #34242

Authored-by: mwish <maplewish117@gmail.com>
Signed-off-by: Will Jones <willjones127@gmail.com>