Fix various clippy warnings

This commit fixes various clippy warnings that do not affect the
function of the code and aren't stylistic in nature.

lib/src/analysis/imsi_requested.rs

@@ -50,7 +50,7 @@ impl Analyzer for ImsiRequestedAnalyzer {
                     event_type: EventType::QualitativeWarning {
                         severity: Severity::High
                     },
-                    message: format!("NAS IMSI identity request detected"),
+                    message: "NAS IMSI identity request detected".to_owned(),
                 })
             }
         }