Investigate use of ArrayPool to reduce allocations

The library is heavily array-dependent, and due to the nature of image handling, we're often allocating very large arrays on the large object heap. The [`ArrayPool`](https://docs.microsoft.com/en-us/dotnet/api/system.buffers.arraypool-1?view=netcore-3.1) API may help alleviate GC overhead.

Useful details discussed here:
https://adamsitnik.com/Array-Pool/