Implement partition path generation (PartitionPathUtils)

[luoyuxia]

Parent Issue

Part of #124 (support partitioned table)
Depends on #126 (BinaryRow deserialization)

Background

Paimon stores data files under partition directories like {table_path}/dt=2024-01-01/hr=12/bucket-0/. Currently there is no code to convert partition values (from BinaryRow) into this filesystem path format.

What needs to be done

1. Create a partition path utility (e.g., spec/partition_utils.rs or similar)

   • Given partition keys (names from TableSchema.partition_keys()) + partition field types (from TableSchema.fields()) + partition values (decoded BinaryRow), generate the partition path string
   • Format: {key1}={value1}/{key2}={value2}/...

2. Handle value formatting per data type

   • Int/BigInt/SmallInt/TinyInt → integer string
   • VarChar/Char/String → string value
   • Date → yyyy-MM-dd format (days since epoch)
   • Timestamp → appropriate timestamp string
   • Boolean → true/false
   • Float/Double → decimal string
   • Decimal → decimal string

3. Handle special cases

   • Null partition values → use __DEFAULT_PARTITION__
   • Special characters in string values → URL encoding if needed (follow Java Paimon's behavior)

4. Unit tests

   • Single partition key
   • Multiple partition keys
   • Different data types (string, int, date)
   • Null partition value → __DEFAULT_PARTITION__

Reference

• Java: PartitionPathUtils

Affected files

• New file: crates/paimon/src/spec/partition_utils.rs (or integrated into existing module)

[QuakeWang]

@luoyuxia plz assign this to me : )