Add integration tests for partitioned table reading

[luoyuxia]

Parent Issue

Part of #124 (support partitioned table)
Depends on #126, #127, #128, #129

Background

Currently, the only integration test (read_log_tables.rs) tests reading a non-partitioned, non-pk append-only table. We need integration tests specifically for partitioned tables.

What needs to be done

1. Prepare test fixtures

   • Create a partitioned table warehouse fixture (or provide instructions to generate one using Java Paimon / Flink)
   • Tables should cover:
     • Single partition key (e.g., dt STRING)
     • Multiple partition keys (e.g., dt STRING, hr INT)
     • Different partition key types (String, Int, Date)

2. Integration tests

   • Read a single-partition-key table, verify all partitions are returned with correct data
   • Read a multi-partition-key table
   • Verify partition column values are correct in the returned RecordBatches

3. Unit tests

   • Test TableScan.plan() on a partitioned table: verify DataSplits have correct bucket_path with partition segments
   • Test that the number of splits matches expected (partition, bucket) groups

Affected files

• crates/integration_tests/tests/ — new test file(s)
• crates/paimon/tests/fixtures/ — possible new fixtures

[luoyuxia]

Merged into a combined issue with #128 and #129