makes DuplicateModuleImport back to an error (#25178)

fixes #24998

Basically it retraces back to the situation before
https://github.com/nim-lang/Nim/pull/18366 and
https://github.com/nim-lang/Nim/pull/18362, i.e.

```nim
import fuzz/a
import fuzz/a
```

```nim
import fuzz/a
from buzz/a
```

```nim
import fuzz/a except nil
from fuzz/a import addInt
```

All of these cases are now flagged as invalid and triggers a
redefinition error, i.e., each module name importing is treated as
consistent as the symbol definition

kinda annoying for importing/exporting with `when conditions` though

ref https://github.com/nim-lang/Nim/issues/18762
https://github.com/nim-lang/Nim/issues/20907

```nim
from std/strutils import toLower
when not defined(js):
  from std/strutils import toUpper
```

(cherry picked from commit 87ee9c84cb)

lib/pure/terminal.nim

@@ -100,7 +100,7 @@ const
   stylePrefix = "\e["
 
 when defined(windows):
-  import std/[winlean, os]
+  import std/os
 
   const
     DUPLICATE_SAME_ACCESS = 2
@@ -926,8 +926,6 @@ when defined(windows):
     stdout.write "\n"
 
 else:
-  import std/termios
-
   proc readPasswordFromStdin*(prompt: string, password: var string):
                             bool {.tags: [ReadIOEffect, WriteIOEffect].} =
     password.setLen(0)
@@ -981,9 +979,6 @@ proc isTrueColorSupported*(): bool =
   ## Returns true if a terminal supports true color.
   return getTerminal().trueColorIsSupported
 
-when defined(windows):
-  import std/os
-
 proc enableTrueColors*() =
   ## Enables true color.
   var term = getTerminal()

lib/system/alloc.nim

@@ -12,7 +12,6 @@
 
 include osalloc
 import std/private/syslocks
-import std/sysatomics
 
 template track(op, address, size) =
   when defined(memTracker):

lib/system/strmantle.nim

@@ -8,9 +8,7 @@
 #
 
 # Compilerprocs for strings that do not depend on the string implementation.
-
-import std/private/digitsutils
-
+import std/private/digitsutils as digitsutils2
 
 proc cmpStrings(a, b: string): int {.inline, compilerproc.} =
   let alen = a.len