fix(loki.source.kubernetes): Forward log lines with out-of-order timestamps

[johnpinto-clarity]

The tailer compared every line with the previous one and skipped the older ones. This dropped stdout lines that containerd wrote after a stderr line with a newer timestamp. Now it only compares with the resume point of the stream, and the saved position moves with the highest timestamp seen. Two tests added: an out-of-order line on a live stream is forwarded, a line older than the resume time is still skipped.

Pull Request Details:
lastReadTime is there to not resend lines after a reconnect (SinceTime has second precision). Moving it on every line made it a filter on the live stream, and Kubernetes does not guarantee order between stdout and stderr in the CRI log file.

Same behaviour kept for the resume: lines before the resume point are skipped, equal ones go through (like #4613). Positions and target.LastEntry use max() so a re-tail never resumes from an older timestamp.

One thing not fixed here: a line out of order exactly at a re-tail boundary can still be lost, a timestamp position cannot tell "already sent" from "written later with an older timestamp". A small slack on the resume point would fix it at the cost of some duplicates per re-tail. Open to do it if you prefer.

Tested in production: 0 of 1435 canary entries lost in 2 hours with this patch, 25 of 717 lost in the same window on a control cluster with the upstream image.

Issue(s) fixed:
Fixes #7076

Notes to the Reviewer

PR Checklist

• Documentation added
• Tests updated
• Config converters updated
• This pull request was substantially generated with AI assistance

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Signed commits report

1 of 1 commit between main and fix/kubetail-out-of-order-lines could not be fully verified:

Commit	Author	Reason	Message
775a2ec5	John Pinto	unknown_key	fix(loki.source.kubernetes): Forward log lines with out-of-order timestamps

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