issues 0033 + 0034: rename repros to focused regression tests

Both repros emit their target diagnostics cleanly today (verified
2026-05-28 against HEAD):

- `issue-0033` → "no visible xx conversion from 's64' to 'Wrap'
  — impl exists in another module but is not imported". Catches
  the case where an `impl Into(X) for Y` is registered globally
  via one module's import chain but is NOT transitively imported
  by the file containing the `xx` site.
- `issue-0034` → "duplicate xx conversion from 's64' to 'Wrap':
  impls in <a> and <b>". Catches two impls covering the same
  (Source, Target) pair both reachable from a single `xx` site.

Renamed to focused feature names:

- `issue-0033*` → `179-impl-visibility*` (4 files: main + impl +
  types + user).
- `issue-0034*` → `180-impl-duplicate*` (4 files: main + impl-a +
  impl-b + types).

Path references inside the files updated. Comment headers tightened
to feature-focused (drop issue-NNNN provenance — that's in git
history now). Expected `.txt` / `.exit` files captured against the
full diagnostic text and exit code 1.

The `issue-*` namespace in `examples/` now shrinks to the literal
list of UNRESOLVED bug repros. 218/218.

tests/expected/179-impl-visibility.txt

@@ -0,0 +1 @@
+/Users/agra/projects/sx/examples/./179-impl-visibility-user.sx:7:17: error: no visible xx conversion from 's64' to 'Wrap' — impl exists in another module but is not imported

tests/expected/180-impl-duplicate.txt

@@ -0,0 +1 @@
+/Users/agra/projects/sx/examples/180-impl-duplicate.sx:20:17: error: duplicate xx conversion from 's64' to 'Wrap': impls in /Users/agra/projects/sx/examples/./180-impl-duplicate-impl-a.sx and /Users/agra/projects/sx/examples/./180-impl-duplicate-impl-b.sx

tests/expected/issue-0033.txt

@@ -1 +0,0 @@
-/Users/agra/projects/sx/examples/./issue-0033-user.sx:7:17: error: no visible xx conversion from 's64' to 'Wrap' — impl exists in another module but is not imported

tests/expected/issue-0034.txt

@@ -1 +0,0 @@
-/Users/agra/projects/sx/examples/issue-0034.sx:11:17: error: duplicate xx conversion from 's64' to 'Wrap': impls in /Users/agra/projects/sx/examples/./issue-0034-impl-a.sx and /Users/agra/projects/sx/examples/./issue-0034-impl-b.sx