* Clean headers pointers when removing links

* Replace the lock

Co-authored-by: Alexey Sharp <alexeysharp@Alexeys-iMac.local>

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* add test

* fix unmarshaling bug

Co-authored-by: Igor Mandrigin <i@mandrigin.ru>

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* mumbai

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Simplify skeleton requests, limit bor spanCache, more fine grained locking in HeaderDownload (#4194)

* Simplify skeleton requests

* Limit bor cache size

* In the middle of changing lists

* Fix

Co-authored-by: Alexey Sharp <alexeysharp@Alexeys-iMac.local>
Co-authored-by: Alex Sharp <alexsharp@Alexs-MacBook-Pro.local>

--nat stun is an automatic external IP detection alternative to manual --nat extip option.
It can be used both at home or on production servers without any extra setup.
It is fast (up to 5 ms) and more reliable than alternatives (as the request goes to the public internet).

This auto-detection is useful to run multiple instances of a service in cloud environments
where the node IPs are not known in advance.

* Reduce insertQueue usage, throttle Skeleton requests

* Cleanup

Co-authored-by: Alexey Sharp <alexeysharp@Alexeys-iMac.local>

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