refactor: restore deprecated peer_id module for backwards compatibility

Address Copilot suggestion to maintain backwards compatibility when migrating
to torrust-peer-id. Downstream code that imports
torrust_tracker_primitives::peer_id::{PeerId, PeerClient} will continue to
work with a deprecation warning, providing a smoother migration path until a
planned major release removes this compatibility layer.

Related-to: PR #1887

Author: josecelano

packages/primitives/src/lib.rs

@@ -9,6 +9,12 @@ pub mod mode;
 pub mod number_of_bytes;
 pub mod pagination;
 pub mod peer;
+#[deprecated(
+    since = "3.0.0-develop",
+    note = "import peer ID types from `torrust_peer_id` crate instead; \
+            this module will be removed in a future release (see EPIC #1669)"
+)]
+pub mod peer_id;
 pub mod policy;
 pub mod scrape;
 pub mod swarm_metadata;
@@ -33,6 +39,15 @@ pub use scrape::ScrapeData;
             this re-export will be removed in a future release (see EPIC #1669)"
 )]
 pub use torrust_clock::DurationSinceUnixEpoch;
+/// **Deprecated**: import from [`torrust_peer_id`] instead via the [`peer_id`] module.
+/// This re-export is kept for backwards compatibility and will be removed in a
+/// future release. Removal is tracked as a follow-up cleanup subissue of EPIC
+/// [#1669](https://github.com/torrust/torrust-tracker/issues/1669).
+#[deprecated(
+    since = "3.0.0-develop",
+    note = "import peer ID types from `torrust_peer_id` crate instead; \
+            this re-export will be removed in a future release (see EPIC #1669)"
+)]
 pub use torrust_peer_id::{PeerClient, PeerId};
 
 /// Network service binding types.

packages/primitives/src/peer_id.rs

@@ -0,0 +1,13 @@
+//! Peer ID types.
+//!
+//! **Deprecated**: import from [`torrust_peer_id`] instead.
+//! This module is kept for backwards compatibility and will be removed in a
+//! future release. Removal is tracked as a follow-up cleanup subissue of EPIC
+//! [#1669](https://github.com/torrust/torrust-tracker/issues/1669).
+
+#[deprecated(
+    since = "3.0.0-develop",
+    note = "import peer ID types from `torrust_peer_id` crate instead; \
+            this module will be removed in a future release (see EPIC #1669)"
+)]
+pub use torrust_peer_id::{PeerClient, PeerId};