Dynamically adjust chunk size

[seanmcguire12]

The motivation for this issue is described in #236, which implemented a temporary fix. We need to implement a more reliable fix for this issue instead of having a set value of 75% of the viewport height. If a sticky banner happens to take up more than 25% of the viewport, then we are still going to be missing candidate elements. Also, if there is no sticky banner, or a very small one, then we are going to be chunking unnecessarily slowly.

Therefore, we need to come up with a solution to dynamically detect sticky/fixed banners on the fly, and then adjust the viewport height accordingly.