integration_tests_sv2 docs cleanup..

- improves wording on `Sniffer` docs, as it implied that messages from upstream are always a response, which is not true
- adds some brief docs to `InterceptMessage` struct
- removes links to private items (which generate warnings on `cargo doc`)

roles/tests-integration/lib/sniffer.rs

@@ -35,21 +35,22 @@ enum SnifferError {
 
 /// Allows to intercept messages sent between two roles.
 ///
+/// Can be useful for testing purposes, as it allows to assert that the roles have sent specific
+/// messages in a specific order and to inspect the messages details.
+///
 /// The downstream (or client) role connects to the [`Sniffer`] `listening_address` and the
 /// [`Sniffer`] connects to the `upstream` server. This way, the Sniffer can intercept messages sent
-/// between the downstream and upstream roles. The downstream will send its messages to the
-/// [`Sniffer`] which will save those in the `messages_from_downstream` aggregator and forward them
-/// to the upstream role. When a response is received it is saved in `messages_from_upstream` and
-/// forwarded to the downstream role. Both `messages_from_downstream` and `messages_from_upstream`
-/// can be accessed as FIFO queues.
+/// between the downstream and upstream roles.
 ///
-/// In order to alter the messages sent between the roles, the [`Sniffer::intercept_messages`]
-/// field can be used. It will look for the [`InterceptMessage::expected_message_type`] in the
-/// specified [`InterceptMessage::direction`] and replace it with
-/// [`InterceptMessage::replace_message`].
+/// Messages received from downstream are stored in the `messages_from_downstream` aggregator and
+/// forward them to the upstream role. Alternatively, messages received from upstream are stored in
+/// the `messages_from_upstream` and forwarded to the downstream role. Both
+/// `messages_from_downstream` and `messages_from_upstream` aggregators can be accessed as FIFO
+/// queues via [`Sniffer::next_message_from_downstream`] and
+/// [`Sniffer::next_message_from_upstream`], respectively.
 ///
-/// Can be useful for testing purposes, as it allows to assert that the roles have sent specific
-/// messages in a specific order and to inspect the messages details.
+/// In order to replace the messages sent between the roles, a set of [`InterceptMessage`] can be
+/// used in [`Sniffer::new`].
 #[derive(Debug, Clone)]
 pub struct Sniffer {
     identifier: String,
@@ -61,6 +62,7 @@ pub struct Sniffer {
     intercept_messages: Vec<InterceptMessage>,
 }
 
+/// Allows [`Sniffer`] to replace some intercepted message before forwarding it.
 #[derive(Debug, Clone)]
 pub struct InterceptMessage {
     direction: MessageDirection,