fix: include precision information in PrecisionTimestamp and Precisio…

…nTimestampTZ literals

BREAKING CHANGE: changes the message type for Literal PrecisionTimestamp and PrecisionTimestampTZ

proto/substrait/algebra.proto

@@ -814,10 +814,8 @@ message Expression {
       VarChar var_char = 22;
       bytes fixed_binary = 23;
       Decimal decimal = 24;
-      // If the precision is 6 or less then this is the microseconds since the UNIX epoch
-      // If the precision is more than 6 then this is the nanoseconds since the UNIX epoch
-      uint64 precision_timestamp = 34;
-      uint64 precision_timestamp_tz = 35;
+      PrecisionTimestamp precision_timestamp = 34;
+      PrecisionTimestamp precision_timestamp_tz = 35;
       Struct struct = 25;
       Map map = 26;
       // Timestamp in units of microseconds since the UNIX epoch.
@@ -859,6 +857,13 @@ message Expression {
       int32 scale = 3;
     }
 
+    message PrecisionTimestamp {
+      // Sub-second precision, 0 means the value given is in seconds, 3 is milliseconds, 6 microseconds, 9 is nanoseconds
+      int32 precision = 1;
+      // Time passed since 1970-01-01 00:00:00.000000 in UTC for PrecisionTimestampTZ and unspecified timezone for PrecisionTimestamp
+      int64 value = 2;
+    }
+
     message Map {
       message KeyValue {
         Literal key = 1;

proto/substrait/type.proto

@@ -36,7 +36,7 @@ message Type {
     FixedBinary fixed_binary = 23;
     Decimal decimal = 24;
     PrecisionTimestamp precision_timestamp = 33;
-    PrecisionTimestampTZ precision_timestamp_tz = 34;
+    PrecisionTimestampTZ precision_timestamp_tz = 34; // value is since UNIX epoch in UTC
 
     Struct struct = 25;
     List list = 27;
@@ -164,13 +164,15 @@ message Type {
   }
 
   message PrecisionTimestamp {
+    // Sub-second precision, 0 means the value given is in seconds, 3 is milliseconds, 6 microsecods, 9 is nanoseconds
     // Defaults to 6
     int32 precision = 1;
     uint32 type_variation_reference = 2;
     Nullability nullability = 3;
   }
 
   message PrecisionTimestampTZ {
+    // Sub-second precision, 0 means the value given is in seconds, 3 is milliseconds, 6 microsecods, 9 is nanoseconds
     // Defaults to 6
     int32 precision = 1;
     uint32 type_variation_reference = 2;