fixes #21393 and misc style changes (#21419)

* fixes #21393 and misc style changes

* progress

---------

Co-authored-by: ringabout <43030857+ringabout@users.noreply.github.com>

lib/std/private/digitsutils.nim

@@ -101,9 +101,7 @@ proc addInt*(result: var string; x: int64) {.enforceNoRaises.} =
         num = cast[uint64](x)
       else:
         num = uint64(-x)
-      let base = result.len
-      setLen(result, base + 1)
-      result[base] = '-'
+      result.add '-'
     else:
       num = uint64(x)
     addInt(result, num)

lib/std/private/ospaths2.nim

@@ -571,7 +571,7 @@ proc normExt(ext: string): string =
 
 proc searchExtPos*(path: string): int =
   ## Returns index of the `'.'` char in `path` if it signifies the beginning
-  ## of extension. Returns -1 otherwise.
+  ## of the file extension. Returns -1 otherwise.
   ##
   ## See also:
   ## * `splitFile proc`_