[C++][Parquet] Reject outlandish values in DELTA_BINARY_PACKED decoder

### Describe the enhancement requested

In `DeltaBitPackDecoder::InitHeader` we're allocating scratch space for miniblock decoding. The size of this scratch space is entirely driven by values read from the [DELTA_BINARY_PACKED header](https://github.com/apache/parquet-format/blob/master/Encodings.md#delta-encoding-delta_binary_packed--5), and could therefore be outlandishly huge.

Given that a huge miniblock size is unlikely to be seen in the wild (and would defeat the point of having miniblocks), we should probably reject non-reasonable values in `InitHeader`.

### Component(s)

C++, Parquet

Locate the C++ implementation of DeltaBitPackDecoder::InitHeader and read how DELTA_BINARY_PACKED header values determine scratch-space allocation. Check the existing Parquet decoder tests, then add coverage showing that unreasonable miniblock sizes are rejected and that normal headers still decode successfully.

Written by the indexing model from the issue text.