ArrowFlightJdbcArray.getArray(index, count) can read past the end of the array slice

`ArrowFlightJdbcArray.checkBoundaries` validates the caller-supplied index against `startOffset + valuesCount`:

```java
private void checkBoundaries(long index, int count) {
if (index < 0 || index + count > this.startOffset + this.valuesCount) {
throw new ArrayIndexOutOfBoundsException();
}
}
```

but `index` is relative to the start of the array; both call sites add `startOffset` to it only afterwards, e.g.

```java
checkBoundaries(index, count);
return getArrayNoBoundCheck(
this.dataVector, LargeMemoryUtil.checkedCastToInt(this.startOffset + index), count);
```

So the accepted range is too large by exactly `startOffset` elements, and `getArray(index, count)` / `getResultSet(index, count)` will read up to that far past the end of the row's slice.

`AbstractArrowFlightJdbcListVectorAccessor` builds these with the offsets of the list element being read, so any row of a list column that does not start at child offset 0 is affected. Reading within the element count the driver itself advertises then returns values belonging to other rows of the shared child vector, and past the child vector's `valueCount` it returns whatever is in allocated-but-unwritten memory.

Reproducer against an `IntVector` of 127 values, with an array covering elements 5..7:

```java
ArrowFlightJdbcArray array = new ArrowFlightJdbcArray(dataVector, 5, 3);
array.getArray(1, 3); // accepted; returns elements 6, 7, 8 — element 8 is outside the array
```

Every existing test constructs the array with `startOffset` 0, where the wrong bound happens to coincide with the correct one, which is why this is not currently caught.

Beginne in ArrowFlightJdbcArray.checkBoundaries und prüfe sowohl die Aufrufstellen von getArray(index, count) als auch von getResultSet(index, count). Füge einen Regressionstest mit einem startOffset ungleich null hinzu, etwa unter Verwendung des bereitgestellten IntVector-Slices, und führe die vorhandenen ArrowFlightJdbcArray-Tests aus; abgeschlossen ist die Änderung, wenn Anfragen nicht über den Array-Slice hinaus lesen können.

Vom Indexierungsmodell aus dem Issue-Text verfasst.