create Datetime3Precision type

Author: angelamayxie

sql/types/datetime.go

@@ -106,6 +106,8 @@ var (
 	Date = MustCreateDatetimeType(sqltypes.Date, 0)
 	// Datetime is a date and a time with default precision (no fractional seconds).
 	Datetime = MustCreateDatetimeType(sqltypes.Datetime, 0)
+	// Datetime3Precision is a date and time with a precision of 3 (fractional seconds to 3 decimal places)
+	Datetime3Precision = MustCreateDatetimeType(sqltypes.Datetime, 3)
 	// DatetimeMaxPrecision is a date and a time with maximum precision
 	DatetimeMaxPrecision = MustCreateDatetimeType(sqltypes.Datetime, MaxDatetimePrecision)
 	// Timestamp is a UNIX timestamp with default precision (no fractional seconds).