f: Clean up chanmon comments and block connection

Restore the module doc sentence stating that a force-close is
considered a fuzz failure, drop comments that restate the code, and
fix inaccurate or duplicated wording around mempool, wallet, and
startup-sync handling.

In connect_chain_range, connect transaction blocks directly instead of
first issuing a best-block update for the empty blocks preceding them;
Confirm explicitly allows skipping intermediary blocks. Also remove an
always-true txdata emptiness check there and a no-op coinbase guard in
apply_tx_to_utxos.

AI tools were used in preparing this commit.

Author: joostjager