fix: stats for timestamp fields for pstats

[nikhilsinhaparseable]

update millisecond timestamp formatting to naive_utc earlier:
ingestion - 2026-04-01T10:31:52.161,
field stats distinct value - 2026-04-01 10:31:52.161 UTC

now:
field stats distinct value - 2026-04-01T10:31:52.161

Summary by CodeRabbit

Release Notes

• Bug Fixes
  • Updated timestamp formatting for millisecond-precision values to ensure consistent and accurate display, with improved handling of invalid timestamps.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 29cbd212-b83f-4fa2-9618-167c610221e6

📥 Commits

Reviewing files that changed from the base of the PR and between a68d90f and beb5b78.

📒 Files selected for processing (1)

• src/storage/field_stats.rs

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Walkthrough

Timestamp formatting for Arrow millisecond timestamps updated in format_arrow_value to use explicit UTC-naive conversion and pattern-based formatting instead of direct string conversion, with unchanged fallback handling for invalid timestamps.

Changes

Cohort / File(s)	Summary
Timestamp Formatting src/storage/field_stats.rs	Modified Arrow millisecond timestamp formatting to convert to UTC-naive datetime and use explicit "%Y-%m-%dT%H:%M:%S%.3f" pattern instead of direct to_string() conversion.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

Poem

🐰 A timestamp once danced in the light,
Now formatted explicit and tight—
UTC-naive, a pattern so clear,
Milliseconds precise without fear!

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description is incomplete; it lacks the standard template sections including issue reference, structured description, and testing/documentation checklist required by the repository.	Add issue reference (Fixes #XXXX), expand description with goal/rationale, and include the testing and documentation checklist from the template.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the main change: fixing timestamp field stats formatting for pstats, which directly aligns with the code modification in format_arrow_value.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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