refactor(db): declare unixepoch instead of formatting a SQL fragment

server/crates/arbiter-server/src/db/functions.rs

@@ -0,0 +1,12 @@
+//! Typed bindings for the SQLite scalar functions used in Diesel expressions.
+
+use diesel::sql_types::{Integer, Text};
+
+diesel::define_sql_function! {
+    /// SQLite `unixepoch(modifier)` -- seconds since the Unix epoch.
+    ///
+    /// Declared so timestamp comparisons are built by the query DSL instead of by
+    /// `format!`-ing a SQL fragment: the argument becomes a bind parameter and the
+    /// result type is checked against the column it is compared with.
+    fn unixepoch(modifier: Text) -> Integer;
+}