GH-1230: fix out-of-bounds write in ClobConsumer buffer growth

[Arawoof06]

What's Changed

ClobConsumer grows the VarCharVector data buffer with a guard on dataBuffer.writerIndex() + bytes.length > capacity(), but it writes each chunk at startIndex + totalBytes through a raw MemoryUtil.copyToMemory that never advances writerIndex(), so the guard stays stuck at offset 0 and reallocDataBuffer() is never called for a CLOB whose bytes exceed the initial ~32KB allocation. The unchecked write then runs past the buffer into adjacent off-heap memory. Both consume paths now check capacity() < startIndex + totalBytes + bytes.length and re-read the buffer after a realloc, matching the sibling BinaryConsumer.

Closes #1230.

[Arawoof06]

gentle ping

[lidavidm]

@Arawoof06 please rebase

[Arawoof06]

Rebased onto main.

[Arawoof06]

Rebased onto current main again. Test/Dev/RC never started any jobs on the August push, and they're waiting on workflow approval for this one.