Test setting size of sizes to less than 8 with chunked datasets

The dataset chunk code uses the configurable "size of sizes" set by H5Pset_sizes for encoding various quantities. However, we do not currently test chunekd datasets with any value other than the default 8. We should add testing for other sizes of sizes (2 and 4), making sure to cover all relevant cases and ensure overflow is detected and handled correctly, and fix any issues that are uncovered by this testing.