Numeric type widening converters

[hemanthsavasere]

Purpose

Linked issue: close #1844

Perform automatic type widening between numeric types when converting POJOs to internal rows. Change from strict and exact type validation to widening conversion from lower to higher data types in POJO field's Java type and the schema's Fluss type.

Implementation Sample Scenarios :
POJO with int field + Schema with BIGINT → SUCCEEDS ✅
POJO with short field + Schema with BIGINT → SUCCEEDS ✅
POJO with int field + Schema with FLOAT → SUCCEEDS ✅
POJO with Long field + Schema with SMALLINT → FAILS (narrowing not supported) ❌

Widening Primitive Conversions :
byte (TINYINT) → short, int, long, float, double
short (SMALLINT) → int, long, float, double
int (INTEGER) → long, float, double
long (BIGINT) → float, double
float (FLOAT) → double

fluss-client

1. Expanded SUPPORTED_TYPES map in ConverterCommons.java to include all widening-compatible source types for each numeric target type
2. Added casting logic in PojoToRowConverter.java with dedicated conversion methods for each numeric type (convertToTinyInt, convertToSmallInt, convertToInteger, convertToBigInt, convertToFloat, convertToDouble)

fluss-flink-common

1. Updated SUPPORTED_TYPES map in PojoToRowConverter.java to include widening-compatible types (both primitives and boxed)
2. Implemented casting logic in createConverterForField() method with corresponding conversion helper methods

Tests

Added comprehensive tests in PojoToRowConverterTest.java for all widening combinations in fluss-client
Added comprehensive tests in PojoToRowConverterTest.java covering all widening scenarios in fluss-flink-common

[hemanthsavasere]

@polyzos Can you please review the pull request. Thanks

[polyzos]

@hemanthsavasere can you remove the documentation? This functionality is meant for internal use.
The goal is to update the existing Java client to use this functionality under the hood so it's transparent to the users.
So we don't need to document it, as it won't be exposed to users directly

[polyzos]

@snuyanzin thank you for reviewing this and your thoughtful feedback

[hemanthsavasere]

@snuyanzin and @polyzos I have done the changes, can you please review PR.

[hemanthsavasere]

@snuyanzin @polyzos I have completed the requested changes. When you have the opportunity, could you please review the PR?