ci: add clippy check to Rust CI workflow (#675)

Add `cargo clippy -- -D warnings` step to the Rust CI job so that
clippy warnings fail the build. Also fix the one new lint
(`unnecessary_map_or`) introduced in the current stable clippy.

Fixes #672

Co-authored-by: hyunjinee <leehj0110@kakao.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

cli/src/native/cdp/chrome.rs

@@ -123,7 +123,7 @@ fn build_chrome_args(options: &LaunchOptions) -> Result<ChromeArgs, String> {
     let has_extensions = options
         .extensions
         .as_ref()
-        .map_or(false, |exts| !exts.is_empty());
+        .is_some_and(|exts| !exts.is_empty());
 
     // Extensions require headed mode in native Chrome (content scripts are not
     // injected in headless mode).  Skip --headless when extensions are loaded.