Address Copilot review nits on PR #461 (round 2)

Apply the genuinely-valid items from the latest GH Copilot
pass; the rest are house-style/local-convenience and get a
reply instead,

- drop the stray space before the colon in
  `test_no_runtime`'s `pytest.raises(...)` (one-off typo).
- drop the unused `cffi` binding in `test_ringbuf` — the
  `importorskip` side-effect is all we need.
- declare the `run-tests` skill's process-cleanup commands
  in `allowed-tools` (`ss`/`pgrep`/`pkill`/`sleep` + a
  scoped `rm -f /tmp/registry@*.sock`).

Review: PR #461 (copilot-pull-request-reviewer)
https://github.com/goodboy/tractor/pull/461#pullrequestreview-4519551472

(this patch was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code

.claude/skills/run-tests/SKILL.md

@@ -16,6 +16,13 @@ allowed-tools:
   - Bash(ls *)
   - Bash(cat *)
   - Bash(jq * .pytest_cache/*)
+  # process inspection + SIGINT-first cleanup ladder (see
+  # the zombie-actor pre-flight / teardown steps below).
+  - Bash(ss *)
+  - Bash(pgrep *)
+  - Bash(pkill *)
+  - Bash(sleep *)
+  - Bash(rm -f /tmp/registry@*.sock)
   - Read
   - Grep
   - Glob

tests/test_ringbuf.py

@@ -6,7 +6,7 @@ import pytest
 import tractor
 
 # XXX `cffi` dun build on py3.14 yet..
-cffi = pytest.importorskip("cffi")
+pytest.importorskip("cffi")
 
 from tractor.ipc._ringbuf import (
     open_ringbuf,