[python] Introduce 'product' aggregator function

[PyRSA]

Purpose

This PR introduces the Python Decimal implementation and aligns the Python FieldProductAgg implementation with the Java implementation.

The changes include:

• Introduce the Python Decimal data structure.
• Support multiplication for all numeric types.
• Add overflow checks for integral types (TINYINT, SMALLINT, INT, BIGINT).
• Support DECIMAL multiplication with precision and scale handling.
• Add comprehensive unit tests.

Tests

• python -m pytest pypaimon/tests/test_decimal.py -q
• python -m pytest pypaimon/tests/test_field_aggregators.py::FieldProductAggTest -q
• python -m pytest pypaimon/tests/test_aggregation_e2e.py -q
• python -m pytest pypaimon/tests/test_aggregation_merge_function.py -q
• git diff --check

[JingsongLi]

Python’s product function does not align with Java semantics. DECIMAL division is silently rounded, whereas Java throws an error; the default decimal precision=28 causes the valid DECIMAL(38,*) operation to fail; FLOAT/DOUBLE division by zero throws an exception, whereas Java returns Infinity; the shared Decimal encoder/decoder also has issues with scale > 18 and negative canonical bytes.

[PyRSA]

Python’s product function does not align with Java semantics. DECIMAL division is silently rounded, whereas Java throws an error; the default decimal precision=28 causes the valid DECIMAL(38,*) operation to fail; FLOAT/DOUBLE division by zero throws an exception, whereas Java returns Infinity; the shared Decimal encoder/decoder also has issues with scale > 18 and negative canonical bytes.

Good catch, thanks! Fixed.
The Python implementation now matches the Java behavior for DECIMAL division and FLOAT/DOUBLE division by zero. It also includes the related Decimal compatibility fixes.

[JingsongLi]

Please resolve conflicts.

[PyRSA]

Please resolve conflicts.

Resolved, thanks!

[PyRSA]

The failure appears to be unrelated to this PR. It is caused by a transient dependency download failure in the paimon-lumina module. I'll wait for CI to be rerun.

Error:  Failed to execute goal on project paimon-lumina: Could not resolve dependencies for project org.apache.paimon:paimon-lumina:jar:2.0-SNAPSHOT: Failed to collect dependencies at org.aliyun.lumina:lumina-jni:jar:0.4.0: Failed to read artifact descriptor for org.aliyun.lumina:lumina-jni:jar:0.4.0: Could not transfer artifact org.aliyun.lumina:lumina-jni:pom:0.4.0 from/to lumina (https://dlf-mvn-repo.oss-cn-shanghai.aliyuncs.com/mvn-repo/release): transfer failed for https://dlf-mvn-repo.oss-cn-shanghai.aliyuncs.com/mvn-repo/release/org/aliyun/lumina/lumina-jni/0.4.0/lumina-jni-0.4.0.pom: Remote host terminated the handshake: SSL peer shut down incorrectly -> [Help 1]
Error:  
Error:  To see the full stack trace of the errors, re-run Maven with the -e switch.
Error:  Re-run Maven using the -X switch to enable full debug logging.
Error:  
Error:  For more information about the errors and possible solutions, please read the following articles:
Error:  [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/DependencyResolutionException
Error:  
Error:  After correcting the problems, you can resume the build with the command
Error:    mvn <args> -rf :paimon-lumina
Error: Process completed with exit code 1.

[JingsongLi]

multiplication is performed outside the high-precision context. The issue still occurs in the latest head: 1234567890123456789 * 1000000000000000001—the trailing digits are truncated.

[PyRSA]

multiplication is performed outside the high-precision context. The issue still occurs in the latest head: 1234567890123456789 * 1000000000000000001—the trailing digits are truncated.

Thanks. Fixed！