fix: validate T-vs-space in incompatible path instead of CORRECTED_COMPATIBLE_FORMATS

Adding the format to CORRECTED_COMPATIBLE_FORMATS made it always go to
GPU, but cuDF's %3f requires exactly 3 fractional digits while CPU
accepts 1-3. This caused ParseDateTimeSuite to fail for inputs like
"1999-12-31 11:59:59.9".

Instead, keep the format on the incompatible path (so it falls back to
CPU without incompatDateFormats) and add targeted validation there:
- Reject inputs with T where the format expects space (fixes #13759)
- Use cuDF isTimestamp to reject truly unparseable strings

Signed-off-by: Allen Xu <allxu@nvidia.com>
Made-with: Cursor

Author: wjxiz1992

sql-plugin/src/main/scala/org/apache/spark/sql/rapids/datetimeExpressions.scala

@@ -607,8 +607,6 @@ object GpuToTimestamp {
       raw"\A\d{2}/\d{2}/\d{4}\Z"),
     "yyyy-MM-dd HH:mm:ss" -> ParseFormatMeta(Option('-'), isTimestamp = true,
       raw"\A\d{4}-\d{2}-\d{2}[ T]\d{2}:\d{2}:\d{2}\Z"),
-    "yyyy-MM-dd HH:mm:ss.SSS" -> ParseFormatMeta(Option('-'), isTimestamp = true,
-      raw"\A\d{4}-\d{2}-\d{2} \d{2}:\d{2}:\d{2}\.\d{3}\Z"),
     "MM-dd" -> ParseFormatMeta(Option('-'), isTimestamp = false,
       raw"\A\d{2}-\d{2}\Z"),
     "MM/dd" -> ParseFormatMeta(Option('/'), isTimestamp = false,
@@ -708,10 +706,26 @@ object GpuToTimestamp {
           }
         }
       case _ =>
-        // this is the incompatibleDateFormats case where we do not guarantee compatibility with
-        // Spark and assume that all non-null inputs are valid
-        withResource(Scalar.fromBool(true)) { s =>
-          ColumnVector.fromScalar(s, col.getRowCount.toInt)
+        // This is the incompatibleDateFormats case where we do not guarantee full
+        // compatibility with Spark. However, we still reject inputs where the
+        // date-time separator doesn't match the format: cuDF treats 'T' and space
+        // as interchangeable, but Spark's DateTimeFormatter requires an exact match.
+        // We also use cuDF isTimestamp to reject truly unparseable strings.
+        if (strfFormat.startsWith("%Y-%m-%d %H") ||
+            strfFormat.startsWith("%Y/%m/%d %H")) {
+          val tProg = new RegexProgram(
+            raw"\A.{10}T", CaptureGroups.NON_CAPTURE)
+          withResource(col.matchesRe(tProg)) { hasT =>
+            withResource(hasT.not()) { noT =>
+              withResource(col.isTimestamp(strfFormat)) { cudfValid =>
+                noT.and(cudfValid)
+              }
+            }
+          }
+        } else {
+          withResource(Scalar.fromBool(true)) { s =>
+            ColumnVector.fromScalar(s, col.getRowCount.toInt)
+          }
         }
     }
   }