Add src/node/* code to node:: namespace

Summary:
Overall PR:

There are no code changes, this is just adding namespace and using declarations and node:: or wallet:: qualifiers in some places.

Motivations for this change are:

• To make it easier to see when node and wallet code is being accessed places where it shouldn't be. For example if GUI code is accessing node and wallet internals or if wallet and node code are referencing each other.
• To make source code organization clearer (core#15732), being able to know that wallet:: code is in src/wallet/, node:: code is in src/node/, init:: code is in src/init/, util:: code is in src/util/, etc.

Notes:

• CBlockIndexWorkComparator is not part of the node namespace for Bitcoin ABC because it is defined in its own header file rather than src/node/blockstorage.h
• some fuzzers and minisketchwrapper.* changes are not applicable due to missing backports (see core#23114).

This is a partial backport of core#23497
https://github.com/bitcoin/bitcoin/pull/23497/commits/90fc8b089d591cabff60ee829a33f96c37fd27ba

Test Plan: ninja all check-all bitcoin-fuzzers bench-bitcoin

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D12763