build: lint "strtol" #40442

Problem:
No lint for strtol().

Solution:
Add lint, and update existing usages.

Callers that previously got a (garbage) large positive value:
- `indent.c`: use getdigits() (intmax, no int truncation) with def=1 so
  overflow/too-large values stay positive and fall through to the
  existing "too big" check (E475).
- `file_search.c`: use getdigits() with def=255 so overflow/too-large
  values keep the "max expand" (else) branch.

The other conversions (api/command.c, eval/window.c, highlight_group.c,
tui/tui.c) only diverge on pathological overflow inputs where strtol's
result was already garbage and the observable outcome is unchanged.

src/nvim/eval/window.c

@@ -9,6 +9,7 @@
 #include "nvim/ascii_defs.h"
 #include "nvim/autocmd.h"
 #include "nvim/buffer.h"
+#include "nvim/charset.h"
 #include "nvim/cursor.h"
 #include "nvim/errors.h"
 #include "nvim/eval/funcs.h"
@@ -277,8 +278,8 @@ static int get_winnr(tabpage_T *tp, typval_T *argvar)
       }
     } else {
       // Extract the window count (if specified). e.g. winnr('3j')
-      char *endp;
-      int count = (int)strtol(arg, &endp, 10);
+      char *endp = (char *)arg;
+      int count = getdigits_int(&endp, false, 0);
       if (count <= 0) {
         // if count is not specified, default to 1
         count = 1;