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GH-44036: [C++] IPC: ipc reader/writer code enhancement (#44019)



### Rationale for this change

So minor ipc code enhancement when I read the code

### What changes are included in this PR?

Avoid copying shared_ptr in some naive space

### Are these changes tested?

Covered by existence

### Are there any user-facing changes?

no

* GitHub Issue: #44036

Authored-by: mwish <maplewish117@gmail.com>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>