[client] Add support of column aliasing for PojoConverter

[VladBanar]

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Motivation

Currently, POJO field names must exactly match Fluss table column names. This creates rigid naming constraints that conflict with Java naming conventions (camelCase) and database naming conventions (snake_case).

Solution

Introduce @ColumnName annotation for POJO fields to map them to table columns with different names. The annotation is processed during POJO inspection in PojoType.of(), storing properties keyed by their mapped column names. This enables seamless bidirectional conversion between POJOs (with idiomatic Java naming) and Fluss tables (with any naming convention), with zero runtime overhead and full backward compatibility.

Anything else?

No response

Willingness to contribute

• I'm willing to submit a PR!