[move-only] Move CAddrMan function definitions to cpp

Summary:

In preparation for introducing the pimpl pattern to addrman, move all function bodies out of the header file.

Partial backport of core#22950:
https://github.com/bitcoin/bitcoin/pull/22950/commits/5faa7dd6d871eac1a0ec5c4a93f2ad7577781a56

Depends on D12326.

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D12327