Fix duplicate field error when partition column already exists in schema

[simbadzina]

Summary

• addPartitionColsToSchema() blindly appends partition columns without checking if they already exist in the schema, causing AvroRuntimeException: Duplicate field X in record
• This can happen when a Hive view projects a partition column as a regular field — the schema already contains the field, and addPartitionColsToSchema() tries to add it again
• The fix collects existing field names into a Set and skips partition columns that are already present

Changes

• SchemaUtilities.addPartitionColsToSchema(): Added deduplication check before adding partition columns
• SchemaUtilitiesTests: Added two tests — one verifying duplicates are skipped, one verifying normal partition column addition still works

Test plan

• New test testAddPartitionColsToSchemaSkipsDuplicates fails without fix, passes with fix
• New test testAddPartitionColsToSchemaAddsNewPartitionCol confirms normal behavior unchanged
• Existing partition tests pass (testBaseTableWithPartition, testSelectStarWithPartition, testSelectPartitionColumn, testUnionSelectStarFromPartitionTable)

[ruolin59]

This shouldn't be needed because partition columns should not exist inside the schema to begin with. Instead of here, it should be fixed on the caller side: if the schema contains the columns, no partition columns should be passed into this method in the first place

[simbadzina]

This shouldn't be needed because partition columns should not exist inside the schema to begin with. Instead of here, it should be fixed on the caller side: if the schema contains the columns, no partition columns should be passed into this method in the first place

The two callers of addPartitionColsToSchema are both inside SchemaUtilities (getCasePreservedSchemaForTable:79 and the merge branch of getAvroSchemaForTable:118-124)

Deduplication in here fit the contract "ensure partition columns are present on the schema".
For some tables the partition columns so already exist in the avro files and then independently in HMS.