move system/atomics out of system; std/atomics should be preferred (#20875)

* move `system/atomics` out of system; `std/atomics` should be preferred

* add deprecation message

* fixes

* fixes

* fixes

* fixes more tests

lib/pure/concurrency/threadpool.nim

@@ -23,7 +23,7 @@ when not compileOption("threads"):
 import cpuinfo, cpuload, locks, os
 
 when defined(nimPreviewSlimSystem):
-  import std/[assertions, typedthreads]
+  import std/[assertions, typedthreads, sysatomics]
 
 {.push stackTrace:off.}
 

lib/pure/nimprof.nim

@@ -24,7 +24,7 @@ when defined(nimHasUsed):
 import hashes, algorithm, strutils, tables, sets
 
 when defined(nimPreviewSlimSystem):
-  import std/syncio
+  import std/[syncio, sysatomics]
 
 when not defined(memProfiler):
   include "system/timers"

lib/pure/oids.nim

@@ -17,6 +17,9 @@
 import hashes, times, endians, random
 from std/private/decode_helpers import handleHexChar
 
+when defined(nimPreviewSlimSystem):
+  import std/sysatomics
+
 type
   Oid* = object ## An OID.
     time: int64