Do not suggest --package when --backend is used, but --build-backend (#10958)

## Summary

Closes #8743

## Test Plan

Snapshot tests

crates/uv-cli/src/lib.rs

@@ -2590,6 +2590,16 @@ pub struct InitArgs {
     #[arg(long, value_enum, conflicts_with_all=["script", "no_package"])]
     pub build_backend: Option<ProjectBuildBackend>,
 
+    /// Invalid option name for build backend.
+    #[arg(
+        long,
+        required(false),
+        action(clap::ArgAction::SetTrue),
+        value_parser=clap::builder::UnknownArgumentValueParser::suggest_arg("--build-backend"),
+        hide(true)
+    )]
+    backend: Option<String>,
+
     /// Do not create a `README.md` file.
     #[arg(long)]
     pub no_readme: bool,

crates/uv/src/settings.rs

@@ -227,6 +227,7 @@ impl InitSettings {
             no_pin_python,
             no_workspace,
             python,
+            ..
         } = args;
 
         let kind = match (app, lib, script) {

crates/uv/tests/it/init.rs

@@ -2253,6 +2253,38 @@ fn init_failure() -> Result<()> {
     Ok(())
 }
 
+#[test]
+fn init_failure_with_invalid_option_named_backend() {
+    let context = TestContext::new("3.12");
+    uv_snapshot!(context.filters(), context.init().arg("foo").arg("--backend"), @r###"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    error: unexpected argument '--backend' found
+
+      tip: a similar argument exists: '--build-backend'
+
+    Usage: uv init [OPTIONS] [PATH]
+
+    For more information, try '--help'.
+    "###);
+    uv_snapshot!(context.filters(), context.init().arg("foo").arg("--backend").arg("maturin"), @r###"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    error: unexpected argument '--backend' found
+
+      tip: a similar argument exists: '--build-backend'
+
+    Usage: uv init [OPTIONS] [PATH]
+
+    For more information, try '--help'.
+    "###);
+}
 #[test]
 #[cfg(feature = "git")]
 fn init_git() -> Result<()> {