[JeonDaehong]

Which issue does this PR close?

• Closes Partition paths format timestamp and binary values differently from iceberg-java #3349.

What changes are included in this PR?

Datum::to_human_string, which partition_to_path uses through Transform::to_human_string, now matches iceberg-java for:

• timestamp / timestamp_ns: yyyy-MM-ddTHH:mm:ss, with trailing zeros of the fraction trimmed (.120000 -> .12, no fraction for whole seconds)
• timestamptz / timestamptz_ns: the same, followed by +00:00
• binary / fixed: standard Base64 with padding

Display for Datum is unchanged, so this only affects partition paths and the partitions.<path> keys in the snapshot summary. Reads are not affected, since they take partition values from manifests. Tables already written by iceberg-rust with these partition types will get the new path format for new files.

Are these changes tested?

Yes.

• New unit tests in transform.rs cover timestamps (micro and nano, with and without zone, whole seconds, trimmed fractions, pre-epoch values) and binary/fixed (empty, padding cases).
• A partition.rs test checks a full path.
• All expected values were produced by running iceberg-java's Transform.toHumanString / PartitionSpec.partitionToPath on main.

cargo test -p iceberg --lib (1845 passed), cargo clippy -p iceberg --all-targets and cargo fmt --check are clean.

AI Disclosure

I used Claude Code to help trace the Rust code path and draft the implementation and tests. I generated the expected values by running iceberg-java myself, and I reviewed the code and ran the tests and lints above.

[JeonDaehong]

@laskoviymishka @kevinjqliu

Hello.
Could you take a look when you have time? This follows the same direction as #3022, aligning to_human_string with iceberg-java, this time for identity-partitioned timestamp and binary values.

Thank you

[JeonDaehong]

Hello. @blackmwk
would you have time to take a look? This aligns timestamp/binary partition paths with iceberg-java, in the same area as #2773. CI is green.

[JeonDaehong]

Rebased on #3358, which changed the same function: to_human_string now handles floats/doubles from #3358 and timestamps/binary from this PR.

[JeonDaehong]

Converted to draft to stay within the new limit of 3 open PRs (#3465). The change is still ready for review; I will mark it ready again when one of my other PRs lands.