Use IEC binary prefixes instead of SI units

I was comparing dcp with dd for a single file, and was initially puzzled by the performance difference with similar block size.

I then realized that dcp prints GB/s when it is actually GiB/s. When this is accounted for, dd and dcp indeed show the same performance.

In accordance to IEEE 1541-2002 and ISO IEC 80000-13 could we modify the following units to use binary prefixes?
https://github.com/hpc/mpifileutils/blob/57a3578b68d8df0fa53a7662c33c6c21ce72400f/src/common/mfu_util.c#L310-L322

This is confusing because other I/O tools use the right unit and print both types of units to show that they are aware of the potential ambiguity:
dd:

419430400 bytes (419 MB, 400 MiB) copied, 0.0436056 s, 9.6 GB/s

See https://github.com/coreutils/coreutils/blob/8d13292a73ecf1f265f77731d3ace29866e3d616/src/dd.c#L588-L591

fio:

   READ: bw=506MiB/s (530MB/s), 506MiB/s-506MiB/s (530MB/s-530MB/s), io=2048MiB (2147MB), run=4049-4049msec

See https://fio.readthedocs.io/en/latest/fio_doc.html#units

Start with the unit-formatting code in src/common/mfu_util.c around lines 310-322, then reproduce dcp's single-file throughput output for comparison. Done means the displayed rates use IEC binary prefixes consistently and no longer label GiB/s values as GB/s.