Hydra::Math: add an exponential_backoff function

t/Math.t

@@ -0,0 +1,19 @@
+use strict;
+use warnings;
+use Setup;
+
+use Hydra::Math qw(exponential_backoff);
+
+use Test2::V0;
+
+subtest "exponential_backoff" => sub {
+    is(exponential_backoff(0), 1);
+    is(exponential_backoff(1), 2);
+    is(exponential_backoff(2), 4);
+    is(exponential_backoff(9), 512);
+    is(exponential_backoff(10), 1024);
+    is(exponential_backoff(11), 1024, "we're clamped to 1024 seconds");
+    is(exponential_backoff(11000), 1024, "we're clamped to 1024 seconds");
+};
+
+done_testing;