fix: prevent 1000 unit prefix output by rolling over on boundary rounding

[AdamMagued]

Summary

When formatting byte values near unit boundaries (such as 999_950 bytes, MByte - Byte, or MiByte - IByte), rounding to the required display precision can produce values equal to the base magnitude (e.g. 1000 kB or 1024 KiB) instead of rolling over to the next unit (1.0 MB or 1.0 MiB).

Root Cause

In humanateBytes:

1. The magnitude index e is determined by math.Floor(logn(float64(s), base)) on the unrounded value.
2. The normalized value val = float64(s) / math.Pow(base, e) is computed and rounded according to minDigits.
3. If val rounds up to base (e.g. 999.95 rounds to 1000.0 with base 1000), no check existed to advance the magnitude index. Consequently, formatting emitted strings such as "1000 kB" or "1024 KiB".

Solution

• After rounding, check if val >= base and an upper unit exists (int(e) < len(sizes)-1).
• If so, advance e++, rescale val /= base, and recompute display precision digits based on the new integer digit count.
• Update test cases expecting unit rollover at boundary conditions and add regression tests for boundary inputs.

Fixes #127

[AdamMagued]

Closing in favor of earlier community PR #160 to avoid duplicate review effort.