Create a reference decode speed benchmark page

[jamsinclair]

Inspiration came from recent references to decode speeds in #44 and #43.

We could likely create a simple benchmark script and HTML page that renders the results. This library is not focused on speed, but it would be convenient to compare speeds between decoding with browser image and canvas APIs vs the WASM decode speed.

[CodeF53]

When making this I would use OffscreenCanvas for the VanillaJS side of the benchmark, as I have found using it tends to have slightly faster results.