Reader does not promote date partition values and column bounds to timestamp / timestamp_ns #3503

Follow-up to #3483. The spec lists date -> timestamp and date -> timestamp_ns as valid v3+ primitive promotions (timestamptz/timestamptz_ns are explicitly not allowed). As with int -> long, the Avro manifest format does not store the type of lower/upper bounds and promotion does not rewrite them, so a value written under date must be decoded and compared using its written type.

iceberg-rust only handles int -> long and float -> double:

Even though this is a latent bug, users don't hit this because iceberg-rust cannot produce this promotion itself today (no column-type update in core), so no user hits it via a round trip. But a date column promoted to timestamp by a v3-capable engine is a valid table that iceberg-rust reads, and such a read would compare date-days against timestamp-micros: wrong pruning and, for a promoted partition source, detached deletes, pretty much the same class of silent mismatch #3483 fixes for int/float.

Possible fix

Teach the value/bound promotion path about the date promotions, ideally as part of moving bound promotion into the reader (the sibling follow-up), so there is one promotion point

Tests

bound pruning where a promoted date column's bounds decide a file; equality-delete / deletion-vector matching across a date -> timestamp promotion; and an overflow case for timestamp_ns asserting a runtime error rather than a wrapped value.