arrow

GH-34802: [C++][Parquet] Allow passing pool to decoder (#34803)



### Rationale for this change

### What changes are included in this PR?

Add `::arrow::MemoryPool` to Decoder builder.

### Are these changes tested?

no

### Are there any user-facing changes?

Parquet user can pass memory pool to decoder now

* Closes: #34802

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