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/system/tmagics.nim

@@ -0,0 +1,66 @@
+discard """
+  matrix: "--mm:refc"
+  output: '''
+true
+true
+false
+true
+true
+false
+true
+'''
+joinable: false
+"""
+
+block tlowhigh:
+  type myEnum = enum e1, e2, e3, e4, e5
+  var a: array[myEnum, int]
+
+  for i in low(a) .. high(a):
+    a[i] = 0
+
+  proc sum(a: openArray[int]): int =
+    result = 0
+    for i in low(a)..high(a):
+      inc(result, a[i])
+
+  doAssert sum([1, 2, 3, 4]) == 10
+
+
+block t8693:
+  type Foo = int | float
+
+  proc bar(t1, t2: typedesc): bool =
+    echo (t1 is t2)
+    (t2 is t1)
+
+  proc bar[T](x: T, t2: typedesc): bool =
+    echo (T is t2)
+    (t2 is T)
+
+  doAssert bar(int, Foo) == false
+  doAssert bar(4, Foo) == false
+  doAssert bar(any, int)
+  doAssert bar(int, any) == false
+  doAssert bar(Foo, Foo)
+  doAssert bar(any, Foo)
+  doAssert bar(Foo, any) == false
+
+block t9442:
+  var v1: ref char
+  var v2: string
+  var v3: seq[char]
+  GC_ref(v1)
+  GC_unref(v1)
+  GC_ref(v2)
+  GC_unref(v2)
+  GC_ref(v3)
+  GC_unref(v3)
+
+block: # bug #6499
+  let x = (chr, 0)
+  doAssert x[1] == 0
+
+block: # bug #12229
+  proc foo(T: typedesc) = discard
+  foo(ref)