fix clippy lints and improve error handling

src/wac_common_ninja.rs

@@ -94,7 +94,8 @@ impl Calendar {
     }
 
     pub(crate) fn read_from_config(config: Config) -> Result<Self> {
-        let s = std::fs::read_to_string(&config.dl.file_path)?;
+        let path = &config.dl.file_path;
+        let s = std::fs::read_to_string(path).with_context(|| format!("Couldn't read {path:?}"))?;
         Self::read_from_str(config, &s)
     }
 }