feat: add timestamp and duration support in leaf data hashing (ITL-438) (#8)

* docs: add design spec for timestamp/duration leaf data hashing (ITL-438)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* docs: add Polars round-trip findings to timestamp/duration hashing spec (ITL-438)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* docs: target main branch in timestamp/duration hashing spec (ITL-438)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* docs: add implementation plan for timestamp/duration hashing (ITL-438)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* feat: add timestamp and duration support in leaf data hashing (ITL-438)

- Add is_timestamp and is_duration checks to _element_size_for_type (8 bytes each)
- Add test_timestamp_types_in_schema and test_duration_types_in_schema
- Add TestTimestampDurationHashing golden parity tests (15 cases)
  matching Rust starfix byte-for-byte

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

---------

Co-authored-by: agent-kurodo[bot] <268466204+agent-kurodo[bot]@users.noreply.github.com>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: kurodo3[bot]