fix: Make cast string to timestamp compatible with Spark

Add addtional formats and handle edge cases.
Update compatibility guide

Author: parthchandra

docs/source/user-guide/latest/compatibility.md

@@ -149,6 +149,15 @@ Cast operations in Comet fall into three levels of support:
   Spark.
 - **N/A**: Spark does not support this cast.
 
+### String to Timestamp
+
+Comet's native `CAST(string AS TIMESTAMP)` implementation supports all timestamp formats accepted
+by Apache Spark, including ISO 8601 date-time strings, date-only strings, time-only strings
+(`HH:MM:SS`), embedded timezone offsets (e.g. `+07:30`, `GMT-01:00`, `UTC`), named timezone
+suffixes (e.g. `Europe/Moscow`), and the full Spark timestamp year range
+(-290308 to 294247). Note that `CAST(string AS DATE)` is only compatible for years between
+262143 BC and 262142 AD due to an underlying library limitation.
+
 ### Legacy Mode
 
 <!--BEGIN:CAST_LEGACY_TABLE-->