complete std prefixes for stdlib (#22887)

follow up https://github.com/nim-lang/Nim/pull/22851
follow up https://github.com/nim-lang/Nim/pull/22873

lib/impure/nre.nim

@@ -61,12 +61,12 @@ runnableExamples:
   assert find("uxabc", re"(?<=x|y)ab", start = 1).get.captures[-1] == "ab"
   assert find("uxabc", re"ab", start = 3).isNone
 
-from pcre import nil
+from std/pcre import nil
 import nre/private/util
-import tables
-from strutils import `%`
-import options
-from unicode import runeLenAt
+import std/tables
+from std/strutils import `%`
+import std/options
+from std/unicode import runeLenAt
 
 when defined(nimPreviewSlimSystem):
   import std/assertions

lib/impure/nre/private/util.nim

@@ -1,5 +1,5 @@
 ## INTERNAL FILE FOR USE ONLY BY nre.nim.
-import tables
+import std/tables
 
 const Ident = {'a'..'z', 'A'..'Z', '0'..'9', '_', '\128'..'\255'}
 const StartIdent = Ident - {'0'..'9'}

lib/impure/rdstdin.nim

@@ -55,7 +55,7 @@ elif defined(genode):
     stdin.readLine(line)
 
 else:
-  import linenoise
+  import std/linenoise
 
   proc readLineFromStdin*(prompt: string, line: var string): bool {.
                           tags: [ReadIOEffect, WriteIOEffect].} =

lib/impure/re.nim

@@ -36,7 +36,7 @@ runnableExamples:
     # can't match start of string since we're starting at 1
 
 import
-  pcre, strutils, rtarrays
+  std/[pcre, strutils, rtarrays]
 
 when defined(nimPreviewSlimSystem):
   import std/syncio