style(cache): give the deferred import's noqa a reason, as the gate requires

`lint` was still red after the format fix, on a different rule this time:

    FAIL: LIT-rule totals exceed their limit (base 1238cfe90f):
      LIT003: total 263 over limit 261 (this change added 1)
        litellm/_service_logger.py:345

LIT003 is `scripts/check_type_discipline.py`'s "noqa requires rule codes or a
reason". The deferred import carried `# noqa: PLC0415` with no reason, so it
counted against the budget; it now says why the import is deferred (a
module-scope import would be circular, since redis_cache imports this module).

Two things worth recording, both found by running the gate rather than guessing:

* A first attempt put the explanation on its own comment line above the import.
  That line contained the word "noqa", which `scan_comments` reads as a *bare*
  suppression -- so the explanatory comment created a second LIT003 instead of
  clearing the first. The reason has to live on the suppression line itself.
* `ruff check` then wanted I001 on the longer line, and its fix wraps the
  import in parentheses with the comment on the imported name.

`ruff format --check`, `ruff check` and the LIT003 scan are all clean on the
three files now, and tests/unit/caching/test_redis_cache.py still reports
100 passed.

litellm/_service_logger.py

@@ -342,7 +342,9 @@ class ServiceLogging(CustomLogger):
             # than at each call site: `redis_cache` hands this hook an exception
             # from ~16 places and a new one must not be able to leak by being
             # written without the redaction.
-            from litellm.caching.redis_cache import redact_redis_error  # noqa: PLC0415
+            from litellm.caching.redis_cache import (
+                redact_redis_error,  # noqa: PLC0415  # redis_cache imports this module; a module-scope import would be circular
+            )
 
             error_message = redact_redis_error(error) if isinstance(error, Exception) else error_message