refactor: reduce needs on cs_main in network processing

[PastaPastaPasta]

Issue being fixed or feature implemented

see: #6953 (comment) -- based on that collected data; the cs_main contention in network processing is ~17% of cs_main contention. If we exclude the islock cs_main (resolved (or mostly resolved don't recall) in that PR) the percentage grows to 30%; if we can minimize contention here, it will benefit our overall cs_main contention data.

What was done?

convert CConman to a structure that is more in line with peerman; namely, objects protect their own internal data, and the vector stores shared pointers, so that we take a shared_ptr from the vector, and then can use it as we desire without lifetime concerns.

Be aware, I would like to upstream these changes, so that we don't have to maintain them long term, however there's no guarantee that will be viable.

How Has This Been Tested?

Deployed testing was minimal; after 6953 is merged; I'd like to deploy this version to some testnet nodes and analyze contention.

Breaking Changes

None

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• I have added or updated relevant unit/integration/functional/e2e tests
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[knst]

can it be atomic?

also fSyncStarted; nBlocksInFlight, fPreferredDownload, fPreferHeaders', fPreferHeadersCmpressed?

[PastaPastaPasta]

Maybe, but need to be more careful that full operation is atomic. I figured just using a mutex currently would be simplier