docs: add missing #[must_use], # Errors, # Panics across public api

hive-ag3nt/src/stats.rs

@@ -29,6 +29,7 @@ pub enum Window {
 }
 
 impl Window {
+    #[must_use]
     pub fn parse(s: &str) -> Self {
         match s {
             "1h" => Self::Hour,
@@ -51,6 +52,7 @@ impl Window {
         }
     }
 
+    #[must_use]
     pub fn span_secs(self) -> i64 {
         match self {
             Self::Hour => 3600,