Add peek and reset methods to Iterator(Inner)

src/root.zig

@@ -1,4 +1,5 @@
 const std = @import("std");
+const assert = std.debug.assert;
 
 pub fn iter(comptime T: type) type {
     return struct {
@@ -76,14 +77,31 @@ pub fn Iterator(comptime Inner: type) type {
 
         pub const Item = Inner.Item;
 
+        pub const capabilities = .{
+            .next = @hasDecl(Inner, "next"),
+            .peek = @hasDecl(Inner, "peek"),
+            .reset = @hasDecl(Inner, "reset"),
+        };
+
         const _Inner = Inner;
 
         const Self = @This();
 
         pub fn next(self: *Self) ?Item {
+            comptime assert(capabilities.next);
             return self.inner.next();
         }
 
+        pub fn peek(self: *Self) ?Item {
+            comptime assert(capabilities.peek);
+            return self.inner.peek();
+        }
+
+        pub fn reset(self: *Self) void {
+            comptime assert(capabilities.reset);
+            return self.inner.reset();
+        }
+
         pub fn map(
             self: Self,
             comptime T: type,