feat: enable decimals in CometFuzzDeltaSuite

Removes the DecimalType exclusion from the fuzz schema generator.
Unlike Iceberg (which excludes decimals due to iceberg-rust
FIXED_LEN_BYTE_ARRAY page-index limitations), Comet's Delta path
handles decimals correctly through the standard ParquetSource reader.

All 7 fuzz tests pass with decimals included (decimal(10,2) and
decimal(36,18) columns in the randomized schema).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: schenksj

spark/src/test/scala/org/apache/comet/CometFuzzDeltaBase.scala

@@ -78,11 +78,7 @@ class CometFuzzDeltaBase extends CometTestBase with AdaptiveSparkPlanHelper {
         SchemaGenOptions(
           generateArray = true,
           generateStruct = true,
-          primitiveTypes = SchemaGenOptions.defaultPrimitiveTypes.filterNot {
-            // Match Iceberg fuzz: exclude DecimalType to avoid known Comet shuffle
-            // hash-function edge cases with high-precision decimals.
-            _.isInstanceOf[DecimalType]
-          }))
+          primitiveTypes = SchemaGenOptions.defaultPrimitiveTypes))
 
       val options =
         DataGenOptions(