Map TIMESTAMP_MILLIS to FROM_UNIXTIME

[tkaunlaky-e6]

Summary

• Refactored TIMESTAMP_MILLIS mapping to use existing UnixToTime expression instead of creating a new class
• Maps Databricks TIMESTAMP_MILLIS(x) to E6 FROM_UNIXTIME_WITHUNIT(x, 'milliseconds')
• Enhanced E6 generator to handle UnixToTime with scale parameter

Changes

1. Removed TimestampMillis class from expressions.py - Avoids unnecessary class proliferation
2. Updated Databricks parser - TIMESTAMP_MILLIS now directly creates UnixToTime with scale='milliseconds'
3. Enhanced E6 generator - from_unixtime_sql now checks for scale parameter and generates FROM_UNIXTIME_WITHUNIT when appropriate

Test plan

• All 857 tests pass
• Existing TIMESTAMP_MILLIS tests verify the transpilation works correctly
• Databricks TIMESTAMP_MILLIS(1230219000123) → E6 FROM_UNIXTIME_WITHUNIT(1230219000123, 'milliseconds')

[gauravdawar-e6]

Looks good!

[ranjanankur314]

Looks good to me.

[gauravdawar-e6]

Looks good