replication: return string when datetime's day or month is 00

[serprex]

MySQL supports 0 for day/month when this is an unknown value

This cannot be encoded into a time.Time, where time.Date normalizes these 0s (so 2000-00-00 would become 1999-11-30)

Pass these values through in their raw string form instead, like we do for 0000-00-00

[Copilot]

Pull Request Overview

This PR updates datetime decoding to preserve zero-valued months or days by returning raw strings instead of normalizing via time.Time.

• Introduces a parseTime flag in decodeDatetime2 and RowsEvent.decodeValue to control string fallback for 00 month/day.
• Renames formatBeforeUnixZeroTime to formatDatetime for unified formatting.
• Adds new tests covering zero‐month/day behavior and adjusts the test harness to iterate parse settings.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
replication/time.go	Renamed formatBeforeUnixZeroTime to formatDatetime.
replication/row_event.go	Updated decodeValue and decodeDatetime2 to use parseTime; handle month==0/day==0 by string.
replication/row_event_test.go	Extended TestDecodeDatetime2 to loop over both parseTime modes and test zero-month/day cases.

Comments suppressed due to low confidence (1)

replication/row_event_test.go:689

• Add test cases with fractional seconds (dec > 0) when month or day is zero to verify that fractional parts are preserved in the string output.

		for _, parseTime := range []bool{true, false} {

[lance6716]

Thanks! I'll start review about 24hrs later.

[dveeden]

Seems fine. But I only glanced over it.