Added serde as an optional dependency

src/record.rs

@@ -1,6 +1,9 @@
+#[cfg(feature = "serde")]
+use serde::{Deserialize, Serialize};
 use chrono::{DateTime, Local, TimeZone};
 
 #[derive(Debug, Clone, Copy, Default, Eq, PartialEq, Ord, PartialOrd, Hash)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 pub enum Clock {
     #[default]
     FirstIn,
@@ -13,6 +16,7 @@ unsafe impl Send for Clock {}
 unsafe impl Sync for Clock {}
 
 #[derive(Debug, Clone, Copy, Default, Eq, PartialEq, Ord, PartialOrd, Hash)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 pub struct Record {
     pub employee_id: u32,
     pub clock: Clock,