Refactor imports in plot.rs tests for macOS compatibility

Reorganized and added conditional imports to improve clarity and maintain consistent functionality across platforms. This ensures the required dependencies are properly included, particularly handling the macOS-specific conditions.

Author: joaquinbejar

plotly/src/plot.rs

@@ -586,10 +586,12 @@ impl PartialEq for Plot {
 mod tests {
     use super::*;
     use crate::Scatter;
-    #[cfg(not(target_os = "macos"))]
-    use base64::engine::general_purpose;
+
     use serde_json::{json, to_value};
     use std::path::PathBuf;
+    #[cfg(not(target_os = "macos"))]
+    use {base64::engine::general_purpose, base64::Engine};
+
     fn create_test_plot() -> Plot {
         let trace1 = Scatter::new(vec![0, 1, 2], vec![6, 10, 2]).name("trace1");
         let mut plot = Plot::new();