Potential message amplification attack

Bifurcation from #219 may be triggered on invalid or potentially invalid network heads coming from headersub. Bifurcation spawns log2(n) amount of header requests sequentially where n is the height of the invalid network head - current subjective head height.

Start by tracing bifurcation when invalid or potentially invalid network heads arrive from headersub, focusing on the sequential header requests it spawns. Determine the conditions that allow request amplification and define a bounded, testable outcome that prevents the reported attack.

Written by the indexing model from the issue text.