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GH-39663: [C++] Ensure top-level benchmarks present informative metrics (#40091)

### Rationale for this change

Some benchmarks may present only an iteration time, or not present sufficiently informative metrics.

### What changes are included in this PR?

Add bytes/second and/or items/second metrics to top-level benchmarks where applicable.

This PR only tackles miscellaneous benchmarks from the top-level Arrow directory, as well as IO, IPC and utilities.

### Are these changes tested?

Manually.

### Are there any user-facing changes?

No.
* Closes: #39663

Authored-by: Antoine Pitrou <antoine@python.org>
Signed-off-by: Antoine Pitrou <antoine@python.org>