Add support for microsecond (6-digit) datetime precision across Eventhouse, Lakehouse, and Shortcuts

[vg78994]

Description:

We are currently using Microsoft Fabric with Eventhouse -> Shortcut -> Lakehouse -> Snowflake Iceberg architecture. We have observed that datetime values are stored with millisecond precision (3 digits), for example:
2025-05-03 08:09:34.301

However, downstream systems like Snowflake Iceberg require microsecond precision (6 digits), such as:
2025-05-03 08:09:34.301000

This mismatch leads to compatibility issues when reading Fabric-generated Parquet files in Iceberg tables.

Current behavior:
Fabric stores datetime values with millisecond precision (scale 3), and there is no built-in way to enforce or convert to microsecond precision.

Expected behavior:
Fabric should support configurable datetime precision (e.g., 3, 6 digits) or automatically pad milliseconds to microseconds when required, ensuring compatibility with downstream systems like Iceberg.

Impact:
This is a critical blocker for integrating Fabric Lakehouse with modern data platforms like Snowflake Iceberg and affects enterprise adoption of Fabric in production environments.