[avalanche] Reduce dependency to net.h from avalanche

Summary:
This diff adds a nodeid.h header to remove the need for the net.h header from avalanche/node.h, and use forward declaration in processor.h. The other header changes come from previously indirectly included headers.

Depends on D9852.

Ref T1634.

Test Plan:

ninja check

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Subscribers: majcosta

Maniphest Tasks: T1634

Differential Revision: https://reviews.bitcoinabc.org/D9853