node: home the peering concept; relocate the connection-retry schedule

Create src/node/peering/ as the home for the peer desired-state
(homeostatic reconciler) concept and move the cross-attempt connection
retry schedule into it: RetryState plus schedule_retry /
schedule_reconnect / process_pending_retries.

Mechanical relocation only. The methods remain inherent on Node; the
retry_count must persist across re-dials (a fresh connection is created
each attempt), which is why the schedule belongs in the peering home
rather than on a per-connection type. The one-level-deeper module path
requires pub(super) -> pub(in crate::node) to preserve the prior scope,
plus module-path fixups at the reference sites. No behavior change; unit
test count unchanged (1596).

src/node/peering/mod.rs

@@ -0,0 +1,12 @@
+//! Peering homeostasis — the desired-state controller for the node's peer set.
+//!
+//! This module is the home for the peering-reconciler concept: config defines a
+//! desired peer set; the reconciler converges the observed set toward it
+//! (auto-connect floor, overlay pool, transport-neighbor growth) under the
+//! `node.limits` ceiling. Startup and steady-state are the same loop.
+//!
+//! The cross-attempt retry schedule (`retry.rs`) lives here because a fresh
+//! connection is created per re-dial, so the escalating backoff count must
+//! persist in the reconciler, not per-connection.
+
+pub(in crate::node) mod retry;