[core] Support streaming LocalKvDb bulk load

[JingsongLi]

Purpose

Support streaming initial bulk load for LocalKvDb without materializing all input entries.

Changes

• Add a BulkLoadWriter API that writes sorted entries directly into bounded-size SST files.
• Publish generated SST files atomically only after finish().
• Require keys to be strictly increasing, so duplicate keys are rejected consistently with RocksDB SST ingestion.
• Clean up all generated files when validation or writing fails.
• Keep the existing iterator API as a checked wrapper around the streaming writer.

Verification

• mvn -q -pl paimon-common -Pfast-build -DwildcardSuites=none '-Dtest=LocalKvDbTest#testBulkLoad+testBulkLoadMultipleSstFiles+testBulkLoadEmptyIterator+testStreamingBulkLoad+testStreamingBulkLoadRejectsDuplicateKeysAndCleansFiles+testBulkLoadValidatesEntryCount+testBulkLoadFailsOnUnsortedEntries+testBulkLoadFailsOnUnorderedSstRanges+testBulkLoadOrderCheckUsesConfiguredComparator' test
• mvn -q -pl paimon-common spotless:check -DskipTests
• mvn -q -pl paimon-common -DskipTests compile

[leaves12138]

Looks good. The streaming writer validates ordering/counts, publishes generated SSTs atomically, and aborts cleanly on failures or early close. LocalKvDbTest passes locally.