fix(helper): handle negative byte counts in get_readable_size

[JSap0914]

Goals:

• Make get_readable_size produce human-readable units for negative byte counts instead of falling back to raw Bytes.

get_readable_size only scales values into KB/MB/GB when num_bytes >= 1024. Because the very first branch is if num_bytes < 1024, every negative value (which is always < 1024) is returned verbatim as Bytes, e.g. get_readable_size(-2 * 1024**2) returns '-2097152 Bytes' instead of '-2.0 MB'.

This actually surfaces in the profiler. jina/logging/profile.py reports a memory delta with get_readable_size(end_mem - start_mem), and that delta is negative whenever memory is freed, so freed-memory deltas are printed as a large raw-byte number rather than a readable size.

Fix:

• Compute the size on abs(num_bytes) and re-apply the original sign to the formatted string. Positive inputs are unchanged.

Verification:

pytest tests/unit/test_helper.py::test_get_readable_size

Result: 9 passed. Added a parametrized regression test covering 0, positive Bytes/KB/MB/GB, and the negative Bytes/KB/MB/GB cases. Before the fix the four negative cases failed (e.g. assert '-2097152 Bytes' == '-2.0 MB'); after the fix they pass.

AI-assisted drafting; changes were reviewed and verified locally by a human before submission.

• check and update documentation

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