[Bug] partition.timestamp-format.strict rejects every DATE partition value #10873

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Paimon version
master @ 5c82868

Compute Engine
Engine-agnostic (core)

Minimal reproduce step

1. Create a table partitioned by dt DATE with partition.timestamp-format.strict=true, partition.timestamp-formatter=yyyy-MM-dd and partition.timestamp-pattern=$dt (the DATE setup documented by [core] Fix expiration of DATE partitions #10464 in manage-partitions.md).
2. Write any row, e.g. dt=2026-10-29.

The write fails with IllegalArgumentException: Partition dt=20755 does not match the 'partition.timestamp-formatter' or 'partition.timestamp-pattern' configuration.

What doesn't meet your expectations?
The documented DATE setup should pass validation. AbstractFileStoreWrite.PartitionTimestampValidator.validate() passes the raw epoch-day integer (20755) to PartitionTimeExtractor instead of the date 2026-10-29.

Anything else?

• Only happens with strict enabled plus an explicit formatter or pattern; default settings are unaffected.
• [core] Fix expiration of DATE partitions #10464 added the same DATE-to-LocalDate conversion only to PartitionExpireStrategy#convertPartition; the write-time validator was not updated.

Are you willing to submit a PR?

• I'm willing to submit a PR!