range: make sure the generic in an integer

src/util/range.zig

@@ -4,6 +4,12 @@ const std = @import("std");
 
 /// Non-inclusive range type over `T`.
 pub fn Range(comptime T: type) type {
+    switch (@typeInfo(T)) {
+        .int => {},
+        else => {
+            @compileError("Range(T) only support integer ranges");
+        },
+    }
     return struct {
         /// Range start.
         start: T,