Fix fractional seconds in RFC3339 timestamps

[fallintoplace]

What does this PR do?

• What: Fix fractional seconds in parse_rfc3339.
• Implementation: Pad short fractions to six digits. Truncate longer fractions.

Motivation

• Why: Valid timestamps like 2019-02-18T16:00:06.123Z raise ValueError. This can stop kubelet pod expiry filtering.

Review checklist (to be filled by reviewers)

• QA decision: qa/required.

[dd-octo-sts]

❌ Dispatcher tests: failed

Dispatcher beta: informational only
Existing CI remains the merge signal.

Caution

2 integrations failed. 4 of 861 jobs failed. Dispatcher could not collect test results for 2 targets.

  861/861 jobs

✅ 857 passed · ❌ 4 failed

Batches · ✅ batch-01 240/240 · ✅ batch-02 219/219 · ❌ batch-03 224/224 · ❌ batch-04 178/178

❌ sap_hana: 2 failed targets

• py3.13-2.0 / linux · batch-03 · step Run the tests · artifacts could not be downloaded
• py3.13-2.0 / linux / minimum base package · batch-03 · step Run the tests · artifacts could not be downloaded

❌ weblogic: 2 failed targets

• py3.13-12 / linux · batch-04 · step Run the tests
• py3.13-14 / linux · batch-04 · step Run the tests

_{Dispatcher finished on 710a7f8 — GitHub Run · Dispatcher Logs.}

[datadog-datadog-prod-us1]

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 89.35% (-0.05%)

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