docs: update Backend and MultiFork docs (#8229)

crates/evm/core/src/backend/mod.rs

@@ -385,6 +385,7 @@ struct _ObjectSafe(dyn DatabaseExt);
 /// snapshot is created before fork `B` is selected, then fork `A` will be the active fork again
 /// after reverting the snapshot.
 #[derive(Clone, Debug)]
+#[must_use]
 pub struct Backend {
     /// The access point for managing forks
     forks: MultiFork,
@@ -417,14 +418,19 @@ pub struct Backend {
 
 impl Backend {
     /// Creates a new Backend with a spawned multi fork thread.
+    ///
+    /// If `fork` is `Some` this will use a `fork` database, otherwise with an in-memory
+    /// database.
     pub fn spawn(fork: Option<CreateFork>) -> Self {
         Self::new(MultiFork::spawn(), fork)
     }
 
     /// Creates a new instance of `Backend`
     ///
-    /// if `fork` is `Some` this will launch with a `fork` database, otherwise with an in-memory
-    /// database
+    /// If `fork` is `Some` this will use a `fork` database, otherwise with an in-memory
+    /// database.
+    ///
+    /// Prefer using [`spawn`](Self::spawn) instead.
     pub fn new(forks: MultiFork, fork: Option<CreateFork>) -> Self {
         trace!(target: "backend", forking_mode=?fork.is_some(), "creating executor backend");
         // Note: this will take of registering the `fork`

crates/evm/core/src/fork/multi.rs

@@ -65,6 +65,7 @@ impl<T: Into<String>> From<T> for ForkId {
 /// The Sender half of multi fork pair.
 /// Can send requests to the `MultiForkHandler` to create forks
 #[derive(Clone, Debug)]
+#[must_use]
 pub struct MultiFork {
     /// Channel to send `Request`s to the handler
     handler: Sender<Request>,
@@ -73,13 +74,6 @@ pub struct MultiFork {
 }
 
 impl MultiFork {
-    /// Creates a new pair multi fork pair
-    pub fn new() -> (Self, MultiForkHandler) {
-        let (handler, handler_rx) = channel(1);
-        let _shutdown = Arc::new(ShutDownMultiFork { handler: Some(handler.clone()) });
-        (Self { handler, _shutdown }, MultiForkHandler::new(handler_rx))
-    }
-
     /// Creates a new pair and spawns the `MultiForkHandler` on a background thread.
     pub fn spawn() -> Self {
         trace!(target: "fork::multi", "spawning multifork");
@@ -109,6 +103,16 @@ impl MultiFork {
         fork
     }
 
+    /// Creates a new pair multi fork pair.
+    ///
+    /// Use [`spawn`](Self::spawn) instead.
+    #[doc(hidden)]
+    pub fn new() -> (Self, MultiForkHandler) {
+        let (handler, handler_rx) = channel(1);
+        let _shutdown = Arc::new(ShutDownMultiFork { handler: Some(handler.clone()) });
+        (Self { handler, _shutdown }, MultiForkHandler::new(handler_rx))
+    }
+
     /// Returns a fork backend
     ///
     /// If no matching fork backend exists it will be created