[flink] Support Blob tables in dedicated split generation

[wwj6591812]

Purpose

Large batch scans can enable scan.dedicated-split-generation to move split planning and emission from the JobManager source coordinator to a dedicated TaskManager operator. This avoids retaining and checkpointing a very large set of split assignments in the JobManager for tables with millions of files.

However, the dedicated reader path did not preserve Blob conversion semantics. ReadOperator always wrapped rows with FlinkRowData, so an internal Blob value was read as byte[] and failed with ClassCastException. This prevented Blob tables from using dedicated split generation.

Changes

• Propagate the physical read type and blob-as-descriptor option from FlinkSourceBuilder through MonitorSource to ReadOperator.
• Use FlinkRowDataWithBlob when the projected read type contains BLOB, ARRAY<BLOB>, or MAP<*, BLOB> fields.
• Keep the existing constructors and MonitorSource.buildSource overload for compatibility.
• Preserve the existing outer projection and field reordering behavior.

Tests

• Added ReadOperatorBlobTest for raw Blob bytes and serialized descriptors.
• Added a Flink integration test covering scan.dedicated-split-generation=true, raw/descriptor modes, projection, and field reordering.
• Flink 1 profile: 3 targeted tests passed, plus 7 related regression tests.
• Flink 2 profile: the same 3 targeted tests passed.
• Checkstyle, Spotless, and git diff --check passed.