rename channels to channels_builtin (#17330)

* improve test coverage for isolation

* a bit better

* rename channels to channels_builtin

lib/pure/collections/deques.nim

@@ -46,7 +46,7 @@ runnableExamples:
 ## See also
 ## ========
 ## * `lists module <lists.html>`_ for singly and doubly linked lists and rings
-## * `channels module <channels.html>`_ for inter-thread communication
+## * `channels module <channels_builtin.html>`_ for inter-thread communication
 
 import std/private/since
 

lib/pure/concurrency/threadpool.nim

@@ -14,7 +14,7 @@
 ## See also
 ## ========
 ## * `threads module <threads.html>`_ for basic thread support
-## * `channels module <channels.html>`_ for message passing support
+## * `channels module <channels_builtin.html>`_ for message passing support
 ## * `locks module <locks.html>`_ for locks and condition variables
 ## * `asyncdispatch module <asyncdispatch.html>`_ for asynchronous IO
 

lib/system.nim

@@ -2385,7 +2385,7 @@ when notJSnotNims and hasAlloc:
     include "system/repr"
 
 when notJSnotNims and hasThreadSupport and hostOS != "standalone":
-  include "system/channels"
+  include "system/channels_builtin"
 
 
 when notJSnotNims and hostOS != "standalone":