Suggest declaring module when trying to use it

Code

After cargo new:

$ git diff --cached
diff --git a/src/foo.rs b/src/foo.rs
new file mode 100644
index 0000000..626450e
--- /dev/null
+++ b/src/foo.rs
@@ -0,0 +1,3 @@
+pub fn hello_world() {
+    println!("hello world");
+}
diff --git a/src/main.rs b/src/main.rs
index e7a11a9..1f8c3d2 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,3 +1,5 @@
+use crate::foo::hello_world;
+
 fn main() {
-    println!("Hello, world!");
+    hello_world()
 }

### Current output

```Shell
$ cargo run
   Compiling import v0.1.0 (/Users/iguridi/repro/import)
error[E0432]: unresolved import `crate::foo`
 --> src/main.rs:1:12
  |
1 | use crate::foo::hello_world;
  |            ^^^ could not find `foo` in the crate root

For more information about this error, try `rustc --explain E0432`.
error: could not compile `import` (bin "import") due to 1 previous error

Desired output

$ cargo run
   Compiling import v0.1.0 (/Users/iguridi/repro/import)
error[E0432]: unresolved import `crate::foo`
 --> src/main.rs:1:12
  |
1 | use crate::foo::hello_world;
  |            ^^^ could not find `foo` in the crate root. Have you declared this module e.g. `mod foo`?

For more information about this error, try `rustc --explain E0432`.
error: could not compile `import` (bin "import") due to 1 previous error

Rationale and extra context

The fix is very easy, but a beginner may miss it

Other cases

No response

Rust Version

$ rustc --version --verbose
rustc 1.76.0 (07dca489a 2024-02-04)
binary: rustc
commit-hash: 07dca489ac2d933c78d3c5158e3f43beefeb02ce
commit-date: 2024-02-04
host: aarch64-apple-darwin
release: 1.76.0
LLVM version: 17.0.6

Anything else?

No response

Reproduce the issue from the src/main.rs and src/foo.rs example by running cargo run, then trace the compiler diagnostic for unresolved import E0432. Done means the diagnostic suggests declaring the missing module, matching the desired output while preserving the existing error information.