.load_with_datetime() is incorrectly rounding to nearest second

[echai58]

Environment

Delta-rs version: 0.14.0

Binding: python

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Bug

What happened:
When you call load_with_datetime, it calls datetime.timestamp(),

delta-rs/crates/deltalake-core/src/table/mod.rs

Line 835 in fee96a7

let target_ts = datetime.timestamp();

- which returns the number of seconds. This is incorrect, because the version history has millisecond granularity

delta-rs/crates/deltalake-core/src/table/mod.rs

Line 180 in fee96a7

created_time: Some(Utc::now().timestamp_millis()),

, so it will return the wrong version if you are trying to read/write at sub-second granularity.

What you expected to happen:
It should call datetime.timestamp_millis().

How to reproduce it:
Write a table, check the transaction time with .history(), and try to read the version as of something in in the same second, but with a greater milliseconds. It will return the incorrect version.