[core] Split chain table batch scans by key range for read parallelism.

[Stephen0421]

Purpose

Chain table batch reads currently produce one split per bucket, which limits read parallelism for large buckets. This PR adds key-range split generation for chain table batch scans:

• Introduces chain-table.split.key-range-enabled (default: true); set to false to fall back to one split per bucket
• Batch scans use IntervalPartition + BinPacking to split snapshot and delta files by key range; files with overlapping key ranges always stay in the same split so all versions of a key across branches are merged correctly
• Streaming reads are unchanged and still use the original one-split-per-bucket behavior

Tests

• Added ChainTableUtilsTest.testBuildChainSplitsWithKeyRangeSplitting: verifies key-disjoint sections are split into separate splits and overlapping snapshot/delta files are kept together
• Added ChainTableUtilsTest.testBuildChainSplitsKeyRangeSplittingLargeTargetKeepsOneSplit: verifies a large targetSplitSize packs all sections into a single split
• Added ChainTableUtilsTest.testBuildChainSplitsWithoutKeyRangeSplitting: verifies a null keyComparator preserves the original one-split-per-bucket behavior

[JingsongLi]

After adding chain-table.split.key-range-enabled, docs/generated/core_configuration.html was not updated.

[Stephen0421]

After adding chain-table.split.key-range-enabled, docs/generated/core_configuration.html was not updated.

OK, fix it.

[JingsongLi]

+1