Fix RegularSession serialization

session_iter/Cargo.toml

@@ -6,4 +6,4 @@ edition = "2021"
 [dependencies]
 chrono = { version = "0.4", features = ["serde"] }
 serde = { version = "1.0", features = ["derive"] }
-clap = { version = "4.5", features = ["derive"] }
+serde_json_any_key = "2.0"

session_iter/src/session.rs

@@ -75,11 +75,10 @@ impl_from!(ExtraSession for Session as Extra);
 pub struct RegularSession {
   pub rule: SessionRule,
   pub note: Note,
+  #[serde(with = "serde_json_any_key::any_key_map")]
   pub except: BTreeMap<Day, Except>,
 }
 
-//TODO we need to implement serialize ourselves, since json doesn't support anything other than string keys
-
 impl From<SessionRule> for RegularSession {
   fn from(rule: SessionRule) -> Self {
     Self {