Stratum v2 connman

[Sjors]

Moved to fork repo from bitcoin#30332 (comment)

Based on bitcoin#30315 and bitcoin#30205. Followed by #49.

Parent PR bitcoin#29432.

This PR introduces Sv2Connman which is somewhat similar to CConnman. It uses the Sv2Transport introduced in bitcoin#30315 to enable incoming connections from other Stratum v2 roles.

It's main target user is the Template Provider role introduced in #49.

There may be other Stratum v2 roles we want to support in the future.

A remaining issue is that the code in ThreadSv2Handler reuses a lot of code from CConnman::SocketHandlerConnected. I'd like to find a way to extract this common functionality and put it somewhere else.

TODO:

• make CConnman::SocketHandlerConnected (partially) reusable
• avoid dependency on bitcoin_node (e.g. move Transport to bitcoin_common)

[Sjors]

@pinheadmz wrote in the original PR:

I am working on a libevent-replacing HTTP server using netbase primitives and yeah, I have some functions that look a lot like the sv2connamn in this branch.

I think it would be cool if possible to abstract the mechanisms in ThreadSocketHandler to work on "abstract clients" and I'd be happy to review and collaborate on that.

I plan to take a look at this.

[Sjors]

CMake rebase.

[Sjors]

Rebased to move everything into a bitcoin_sv2 library (use -DWITH_SV2=ON to compile).