Review and improve bid timeout logic

[dgirardi]

Type of issue

Bug

Description

See #10320 (comment) for details - breaking this out into its own issue:

There are several problems with the timeout logic:

• the 2nd mechanism (using timeToRespond) appears to be entirely redundant. I suspect it's a relic.
• the 1st mechanism does not look at timeoutBuffer, which is different from what we say in the docs.
• a bid request can be considered "late" when it isn't, if it's routed to Prebid Server and there's no client side adapter for it.