fix #13218: avoid some irrelevant warnings for nim doc,rst2html,--app:lib, + other fixes (#13550)

* fix #13218: avoid some irrelevant warnings for nim doc,rst2html
* suppress warnRedefinitionOfLabel for nim doc
* lots of fixes for UnusedImport warnings

lib/pure/asyncdispatch.nim

@@ -168,7 +168,7 @@
 
 include "system/inclrtl"
 
-import os, tables, strutils, times, heapqueue, lists, options, asyncstreams
+import os, tables, strutils, times, heapqueue, options, asyncstreams
 import options, math, std/monotimes
 import asyncfutures except callSoon
 

lib/pure/asynchttpserver.nim

@@ -30,7 +30,7 @@
 ##
 ##    waitFor server.serve(Port(8080), cb)
 
-import tables, asyncnet, asyncdispatch, parseutils, uri, strutils
+import asyncnet, asyncdispatch, parseutils, uri, strutils
 import httpcore
 
 export httpcore except parseHeader

lib/pure/encodings.nim

@@ -10,7 +10,7 @@
 ## Converts between different character encodings. On UNIX, this uses
 ## the `iconv`:idx: library, on Windows the Windows API.
 
-import os, parseutils, strutils
+import os
 
 when not defined(windows):
   type
@@ -28,6 +28,7 @@ type
                                         ## for encoding errors
 
 when defined(windows):
+  import parseutils, strutils
   proc eqEncodingNames(a, b: string): bool =
     var i = 0
     var j = 0

lib/pure/lenientops.nim

@@ -24,8 +24,6 @@
 ## either casting to float or rounding to int might be preferred, and users
 ## should make an explicit choice.
 
-import typetraits
-
 proc `+`*[I: SomeInteger, F: SomeFloat](i: I, f: F): F {.noSideEffect, inline.} =
   F(i) + f
 proc `+`*[I: SomeInteger, F: SomeFloat](f: F, i: I): F {.noSideEffect, inline.} =

lib/pure/selectors.nim

@@ -27,7 +27,7 @@
 ##
 ## TODO: ``/dev/poll``, ``event ports`` and filesystem events.
 
-import os, strutils, nativesockets
+import os, nativesockets
 
 const hasThreadSupport = compileOption("threads") and defined(threadsafe)
 
@@ -230,6 +230,7 @@ when defined(nimdoc):
     ## For *poll* and *select* selectors ``-1`` is returned.
 
 else:
+  import strutils
   when hasThreadSupport:
     import locks
 

lib/pure/strformat.nim

@@ -744,8 +744,6 @@ when isMainModule:
   check &"{high(int64)}", "9223372036854775807"
   check &"{low(int64)}", "-9223372036854775808"
 
-  import json
-
   doAssert fmt"{'a'} {'b'}" == "a b"
 
   echo("All tests ok")