prometheus: Fix formatBytes invalid output

[skools-here]

Summary

This PR addresses an issue where the formatBytes utility function produces invalid output strings (such as NaNundefined) when it receives negative, NaN, or non-finite inputs.

Fixes: #853

Problem

In prometheus/src/util.ts, the formatBytes function calculates the logarithm of the input to determine the formatting scale (KB, MB, etc.). However, when the input is:

• Negative (e.g., -1): Math.log(-1) returns NaN, leading to NaNundefined UI outputs. This case frequently arises briefly during counter resets or delta calculations in Prometheus metrics.
• NaN / Infinity: The scaling calculation evaluates to NaN or out-of-bounds indices, causing the UI to render NaNundefined.

Solution

• Input Validation: Added validation in formatBytes to return a graceful fallback of "0.00B" if the input is negative (bytes < 0) or not finite (!Number. isFinite(bytes)). This aligns with the formatting of 0 bytes.
• Unit Tests: Added test coverage in util.test.ts to verify the handling.

[skools-here]

ptal @illume