fix(stats): reject non-positive bandwidth polling intervals [skip changelog]

[wangjingshuiku]

Summary

• Reject zero and negative polling intervals in ipfs stats bw.
• Add CLI regression coverage for 0s and -1s.

Motivation

time.ParseDuration accepts non-positive durations. With --poll, passing --interval=0s or --interval=-1s makes time.After immediately ready, causing stats bw to repeatedly collect and emit bandwidth statistics without waiting.

The command now returns:

interval must be greater than zero

for non-positive intervals.

Testing

• make build
• go test ./test/cli -run '^TestStats$' -count=1 -v
• go test ./core/commands -run '^$'
• git diff --check