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/packages/docutils/dochelpers.nim

@@ -13,7 +13,8 @@
 ## `type LangSymbol`_ in ``rst.nim``, while `match(generated, docLink)`_
 ## matches it with `generated`, produced from `PNode` by ``docgen.rst``.
 
-import rstast, strutils
+import rstast
+import std/strutils
 
 when defined(nimPreviewSlimSystem):
   import std/[assertions, syncio]

lib/packages/docutils/highlite.nim

@@ -57,8 +57,8 @@
 ## as program output.
 
 import
-  strutils
-from algorithm import binarySearch
+  std/strutils
+from std/algorithm import binarySearch
 
 when defined(nimPreviewSlimSystem):
   import std/[assertions, syncio]

lib/packages/docutils/rst.nim

@@ -21,8 +21,10 @@
 ## turned on by passing ``options:`` [RstParseOptions] to [proc rstParse].
 
 import
-  os, strutils, rstast, dochelpers, std/enumutils, algorithm, lists, sequtils,
-  std/private/miscdollars, tables, strscans, rstidx
+  std/[os, strutils, enumutils, algorithm, lists, sequtils,
+  tables, strscans]
+import dochelpers, rstidx, rstast
+import std/private/miscdollars
 from highlite import SourceLanguage, getSourceLanguage
 
 when defined(nimPreviewSlimSystem):

lib/packages/docutils/rstast.nim

@@ -9,7 +9,7 @@
 
 ## This module implements an AST for the `reStructuredText`:idx: parser.
 
-import strutils, json
+import std/[strutils, json]
 
 when defined(nimPreviewSlimSystem):
   import std/assertions

lib/packages/docutils/rstgen.nim

@@ -39,10 +39,10 @@
 ##   No backreferences are generated since finding all references of a footnote
 ##   can be done by simply searching for ``[footnoteName]``.
 
-import strutils, os, hashes, strtabs, rstast, rst, rstidx,
-  highlite, tables, sequtils,
-  algorithm, parseutils, std/strbasics
+import std/[strutils, os, hashes, strtabs, tables, sequtils,
+  algorithm, parseutils, strbasics]
 
+import rstast, rst, rstidx, highlite
 
 when defined(nimPreviewSlimSystem):
   import std/[assertions, syncio, formatfloat]

lib/packages/docutils/rstidx.nim

@@ -7,8 +7,8 @@
 
 ## Nim `idx`:idx: file format related definitions.
 
-import strutils, std/syncio, hashes
-from os import splitFile
+import std/[strutils, syncio, hashes]
+from std/os import splitFile
 
 type
   IndexEntryKind* = enum ## discriminator tag