quality audit: fix dsu_weighted sentinel precision; fix comment typo (#227)

Co-authored-by: Cameron Custer <cam@augmentcode.com>

Author: cameroncuster

library/data_structures_[l,r)/uncommon/deque_op.hpp

@@ -3,7 +3,7 @@
 //! @code
 //!   deq dq(a, ranges::min);
 //! @endcode
-//! @time operations are O(1) ammortized
+//! @time operations are O(1) amortized
 //! @space O(n)
 template<class T, class F> struct deq {
   using dt = array<T, 2>;

library/dsu/dsu_weighted.hpp

@@ -19,7 +19,7 @@ struct dsu_weighted {
   }
   int size(int u) { return -p[f(u)]; }
   ll diff(int u, int v) {
-    return f(u) == f(v) ? d[v] - d[u] : 1e18;
+    return f(u) == f(v) ? d[v] - d[u] : ll(1e18);
   }
   bool join(int u, int v, ll w) {
     int x = f(u), y = f(v);