some test cleanups & category reorganization (#22010)

* clean up some test categories

* mention exact slice issue

* magics into system

* move trangechecks into overflow

* move tmemory to system

* try fix CI

* try fix CI

* final CI fix

tests/global/a_module.nim

@@ -0,0 +1,6 @@
+# a.nim
+{.push stackTrace: off.}
+proc foo*(): int =
+  var a {.global.} = 0
+  result = a
+{.pop.}

tests/global/tglobal2.nim

@@ -0,0 +1,7 @@
+discard """
+output: "0"
+"""
+
+# b.nim
+import a_module
+echo foo()