make more standard libraries work with nimPreviewSlimSystem (#20343)

* make more standard libraries work with `nimPreviewSlimSystem`

* typo

* part two

* Delete specutils.nim

* fixes more tests

* more fixes

* fixes tests

* fixes three more tests

* add formatfloat import

* fix

* last

lib/std/jsbigints.nim

@@ -3,6 +3,9 @@
 when not defined(js):
   {.fatal: "Module jsbigints is designed to be used with the JavaScript backend.".}
 
+when defined(nimPreviewSlimSystem):
+  import std/assertions
+
 type JsBigIntImpl {.importjs: "bigint".} = int # https://github.com/nim-lang/Nim/pull/16606
 type JsBigInt* = distinct JsBigIntImpl         ## Arbitrary precision integer for JavaScript target.
 

lib/std/sysrand.nim

@@ -62,6 +62,9 @@ when not defined(js):
 when defined(posix):
   import posix
 
+when defined(nimPreviewSlimSystem):
+  import std/assertions
+
 const
   batchImplOS = defined(freebsd) or defined(openbsd) or defined(zephyr) or (defined(macosx) and not defined(ios))
   batchSize {.used.} = 256

lib/std/tasks.nim

@@ -13,6 +13,9 @@
 import std/[macros, isolation, typetraits]
 import system/ansi_c
 
+when defined(nimPreviewSlimSystem):
+  import std/assertions
+
 export isolation
 
 

lib/std/tempfiles.nim

@@ -19,6 +19,8 @@ See also:
 
 import os, random
 
+when defined(nimPreviewSlimSystem):
+  import std/syncio
 
 const
   maxRetry = 10000