[WIP] [core] Introduce BLOB_REF for shared blob data

[leaves12138]

Purpose

This PR introduces BLOB_REF for sharing blob data across tables without duplicating payloads in Paimon-managed storage.

Changes

• add the BLOB_REF type and wire it through API, format, Arrow, Flink, Spark and Hive type conversions
• serialize BLOB_REF values as BlobReference metadata instead of inline blob payloads
• resolve blob references lazily on read, preferring direct URI reads and falling back to metadata lookup by table/row/field
• keep the fallback path streaming instead of buffering the whole blob into memory
• add fieldId to blob references for better schema evolution compatibility during fallback lookup
• avoid dereferencing blob payloads in InternalRowToSizeVisitor
• explicitly reject nested BLOB_REF in schema validation, since read-time resolution currently only supports top-level BLOB_REF
• add unit tests for blob reference serialization, fallback streaming, size estimation, schema validation and fallback lookup

Testing

Passed:

• mvn -pl paimon-common -am -DfailIfNoTests=false -Dcheckstyle.skip -Dspotless.check.skip -Denforcer.skip -Dtest=BlobReferenceTest,BlobReferenceBlobTest,InternalRowToSizeVisitorTest test

[leaves12138]

I found a few runtime gaps where BLOB_REF support is still incomplete.