Add more correctness checks to network analyzer

[patrickhulce]

Summary
There's a lot of estimates happening in network-analyzer. We can sanity check more of these to make sure there's nothing fishy going on.

• In estimateIfConnectionWasReused, compute the maximum number of parallel requests (N) and ensure we have at least N requests that required new connections.
• Expand the findMainDocument handling of edge cases

[patrickhulce]

I'm no longer convinced this is worth pursuing.

In estimateIfConnectionWasReused, compute the maximum number of parallel requests (N) and ensure we have at least N requests that required new connections.

In general prevalence of H2 has made this much less relevant and we've moved away from fatal errors when things seem just a little fishy (🎉). It's not clear what we action Lighthouse would take if our estimates determined there were only N-1 available connections instead of N.

Expand the findMainDocument handling of edge cases

Definitely worth doing, but super complicated and I'm already addressing pieces as we go for #8984

I'll close for now.