chore: checkpoint before Python removal

vendor/tower/src/limit/rate/rate.rs

@@ -0,0 +1,30 @@
+use std::time::Duration;
+
+/// A rate of requests per time period.
+#[derive(Debug, Copy, Clone)]
+pub struct Rate {
+    num: u64,
+    per: Duration,
+}
+
+impl Rate {
+    /// Create a new rate.
+    ///
+    /// # Panics
+    ///
+    /// This function panics if `num` or `per` is 0.
+    pub const fn new(num: u64, per: Duration) -> Self {
+        assert!(num > 0);
+        assert!(per.as_nanos() > 0);
+
+        Rate { num, per }
+    }
+
+    pub(crate) fn num(&self) -> u64 {
+        self.num
+    }
+
+    pub(crate) fn per(&self) -> Duration {
+        self.per
+    }
+}