iter 23.2.3-prep: reconcile workspace tests with auto-loaded prelude class Eq

The auto-loaded prelude (iter 23.2 work-in-progress) injects
`class Eq` plus three primitive instances (Eq Int, Eq Bool, Eq Str)
into every workspace. Five workspace::tests assertions broke against
this new baseline:

- iter22b1_missing_method_fires_diagnostic
- instance_without_superclass_instance_fires
- instance_overriding_nonexistent_method_fires
  Their fixtures redeclare `class Eq` (and `class Ord` in one case),
  which now collides with the prelude. Renamed each fixture's
  `Eq`/`eq` -> `TEq`/`teq` and `Ord`/`lt` -> `TOrd`/`tlt`, matching
  the scheme already used in the two earlier-renamed test_22b2
  fixtures. Method `ne` stays (does not collide). Assertion strings
  in workspace.rs updated to match.

- iter22b1_workspace_with_no_classes_has_empty_registry
- iter22b1_instance_in_class_module_loads_clean
  Their asserted registry counts assumed an otherwise-empty registry.
  Rewritten to filter by `defining_module != "prelude"`: the property
  is "no NON-prelude entries" / "exactly one fixture-owned entry",
  not raw count.

Doc comments updated alongside each assertion change so the rationale
for TEq/TOrd (collision avoidance) is local. No production code
touched.

examples/test_22b1_missing_method.ail.json

@@ -5,11 +5,11 @@
   "defs": [
     {
       "kind": "class",
-      "name": "Eq",
+      "name": "TEq",
       "param": "a",
       "methods": [
         {
-          "name": "eq",
+          "name": "teq",
           "type": {
             "k": "fn",
             "params": [
@@ -36,7 +36,7 @@
     },
     {
       "kind": "instance",
-      "class": "Eq",
+      "class": "TEq",
       "type": { "k": "con", "name": "Int" },
       "methods": [
         {