[core] Fix record comparator cache key for sort order

[Liulietong]

Problem

The cache key for recordComparator only considered the sort key types but ignored the sort order (ascending/descending). This caused comparators with different sort orders to share the same cached class, leading to incorrect sorting behavior.

Solution

Include SortOrder in the cache key generation to ensure each unique sort order combination gets its own generated comparator class.

Summary

• Include sort order in the codegen cache key for record comparators
• Add a regression test for ascending/descending comparator cache collisions

Testing

mvn -pl paimon-core -Dtest=CodeGenUtilsTest test

[Liulietong]

Hi @JingsongLi, could you help review this PR? It's a fix for the record comparator cache key to include sort order. Thanks!