Use more Natural and Positive numbers in proc parameters

- Didn't go through all modules, only the main ones I thought of
- Building the compiler and tests still work

lib/pure/collections/sets.nim

@@ -114,7 +114,7 @@ proc mustRehash(length, counter: int): bool {.inline.} =
   assert(length > counter)
   result = (length * 2 < counter * 3) or (length - counter < 4)
 
-proc rightSize*(count: int): int {.inline.} =
+proc rightSize*(count: Natural): int {.inline.} =
   ## Return the value of `initialSize` to support `count` items.
   ##
   ## If more items are expected to be added, simply add that