build: treat clang-tidy warnings as errors (neovim#22238)

.clang-tidy

@@ -1,3 +1,4 @@
+WarningsAsErrors: '*'
 Checks: >
   -*,
 

src/nvim/eval.c

@@ -3410,7 +3410,7 @@ static int eval_index(char **arg, typval_T *rettv, int evaluate, int verbose)
         if (n1 >= len || n2 < 0 || n1 > n2) {
           v = NULL;
         } else {
-          v = xmemdupz(s + n1, (size_t)(n2 - n1 + 1));
+          v = xmemdupz(s + n1, (size_t)n2 - (size_t)n1 + 1);
         }
       } else {
         // The resulting variable is a string of a single

src/nvim/ops.c

@@ -923,7 +923,7 @@ int do_record(int c)
     dict_T *dict = get_v_event(&save_v_event);
 
     // The recorded text contents.
-    char *p = (char *)get_recorded();
+    char *p = get_recorded();
     if (p != NULL) {
       // Remove escaping for K_SPECIAL in multi-byte chars.
       vim_unescape_ks(p);