fix: avoid potential divide-by-zero in network hashrate stats calculation

[kwvg]

Additional Information

It was reported that on occasion, network.*hashesPerSecond would report NaN gauge values, which would be dismissed as malformed reporting by Grafana (see below). Those gauges use a simplified version (source) of GetNetworkHashPS (source), crucially, without a check meant to avoid divide-by-zeros (source).

Error log (courtesy of PastaPastaPasta):

[...]
graphite-1             | 7 Dec 21:18:05 - DEBUG: Bad line: -nan,g in msg "network.terahashesPerSecond:-nan|g"
graphite-1             | 7 Dec 21:18:05 - DEBUG: Bad line: -nan,g in msg "network.petahashesPerSecond:-nan|g"
graphite-1             | 7 Dec 21:18:05 - DEBUG: Bad line: -nan,g in msg "network.exahashesPerSecond:-nan|g"
graphite-1             | 7 Dec 21:18:10 - DEBUG: Bad line: -nan,g in msg "network.hashesPerSecond:-nan|g"
graphite-1             | 7 Dec 21:18:10 - DEBUG: Bad line: -nan,g in msg "network.terahashesPerSecond:-nan|g"
graphite-1             | 7 Dec 21:18:10 - DEBUG: Bad line: -nan,g in msg "network.petahashesPerSecond:-nan|g"
graphite-1             | 7 Dec 21:18:10 - DEBUG: Bad line: -nan,g in msg "network.exahashesPerSecond:-nan|g"
graphite-1             | 7 Dec 21:18:15 - DEBUG: Bad line: -nan,g in msg "network.hashesPerSecond:-nan|g"
[...]

This has been resolved by adding that check, alongside encapsulating the logic in a lambda and not reporting the gauge values if the estimated hashes per second reported is zero, due to the unlikelihood of it being correct.

Breaking Changes

None expected.

Checklist

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas (note: N/A)
• I have added or updated relevant unit/integration/functional/e2e tests (note: N/A)
• I have made corresponding changes to the documentation (note: N/A)
• I have assigned this pull request to a milestone (for repository code-owners and collaborators only)

[kwvg]

Special thanks to @PastaPastaPasta for reporting this issue

[UdjinM6]

utACK 40070c0

[knst]

utACK 40070c0