Partial workaround and deprecation warning for breaking change usage of #15654 (#15806)

# Description
Adds a temporary workaround to prevent #15654 from being a breaking
change when using a closure stored in a variable, and issues a warning.
Also has a special case related to
https://github.com/carapace-sh/carapace-bin/pull/2796 which suggests
re-running `carapace init`


![image](https://github.com/user-attachments/assets/783f3dbf-2a85-4aa5-ac66-efc584ac77fd)


![image](https://github.com/user-attachments/assets/c8fb5ae1-66a8-474c-8244-a22600f4da43)

# After Submitting
Remove variable name detection after grace period

crates/nu-protocol/src/errors/shell_error/mod.rs

@@ -1219,12 +1219,12 @@ This is an internal Nushell error, please file an issue https://github.com/nushe
         span: Span,
     },
 
-    #[error("{deprecated} is deprecated and will be removed in a future release")]
-    #[diagnostic()]
-    Deprecated {
-        deprecated: &'static str,
-        suggestion: &'static str,
-        #[label("{deprecated} is deprecated. {suggestion}")]
+    #[error("{deprecation_type} deprecated.")]
+    #[diagnostic(code(nu::shell::deprecated))]
+    DeprecationWarning {
+        deprecation_type: &'static str,
+        suggestion: String,
+        #[label("{suggestion}")]
         span: Span,
         #[help]
         help: Option<&'static str>,