[Java][JDBC] ClobConsumer writes past VarCharVector data buffer for large CLOBs

ClobConsumer copies CLOB data into the VarCharVector data buffer with `MemoryUtil.copyToMemory` at offset `startIndex + totalBytes`, but the buffer-growth guard checks `dataBuffer.writerIndex() + bytes.length > dataBuffer.capacity()`. `copyToMemory` never advances `writerIndex()`, and nothing else does either, so it stays at 0 and the guard only ever checks that a single chunk fits at offset 0. Once the cumulative bytes of a CLOB (or a batch of CLOB rows) exceed the initial data-buffer allocation of about 32 KB, `reallocDataBuffer()` is never called and `copyToMemory`, which performs no ArrowBuf bounds checking, writes past the allocation into adjacent off-heap memory.

The sibling `BinaryConsumer` uses the correct check: `while (vector.getDataBuffer().capacity() < (startOffset + dataLength + read))`.

To reproduce, consume a single CLOB whose UTF-8 length exceeds the initial data buffer (for example `INITIAL_VALUE_ALLOCATION * 8 * 4` characters). The out-of-bounds write corrupts the adjacent offset buffer, and reading the value back throws `NegativeArraySizeException`.

ClobConsumer を特定し、その VarCharVector のデータバッファ拡張ガードを、対応する BinaryConsumer のチェックと比較します。UTF-8 データが初期割り当てを超える CLOB で再現し、その後、累積した CLOB またはバッチデータによってオフセットバッファが破損せず、正常に読み戻せることを確認します。

索引モデルが issue の本文から書いたものです。