add -d:nimStrictMode in CI to keep code from regressing; fixes ConvFromXtoItselfNotNeeded, UnusedImport notes (#16764)

lib/std/monotimes.nim

@@ -74,7 +74,7 @@ when defined(js):
     system.`+`(a, b)
   {.pop.}
 
-elif defined(posix):
+elif defined(posix) and not defined(osx):
   import posix
 
 elif defined(windows):

lib/std/private/globs.nim

@@ -4,7 +4,9 @@ this can eventually be moved to std/os and `walkDirRec` can be implemented in te
 to avoid duplication
 ]##
 
-import std/[os,strutils]
+import std/[os]
+when defined(windows):
+  from strutils import replace
 
 type
   PathEntry* = object