[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`.

定位 ClobConsumer，并将其 VarCharVector 数据缓冲区增长保护与 BinaryConsumer 中对应的检查进行比较。使用 UTF-8 数据超过初始分配大小的 CLOB 重现该问题，然后验证累积的 CLOB 或批处理数据不会损坏偏移缓冲区，并且可以成功读回。

由索引模型根据 Issue 内容生成。