Fix clippy warnings

src/trace.rs

@@ -12,6 +12,9 @@ use crate::error::error_from_sqlite_code;
 use crate::{Connection, Result};
 
 /// Set up the process-wide SQLite error logging callback.
+///
+/// # Safety
+///
 /// This function is marked unsafe for two reasons:
 ///
 /// * The function is not threadsafe. No other SQLite calls may be made while