test(io-metrics): assert record helper emissions; fix census heuristic (#6217)

* test(io-metrics): assert lib.rs record helper emissions

The 29 assertion-less record_* smoke tests in io-metrics/src/lib.rs called
their helpers and checked nothing; because METRICS_ENABLED defaults to
false they did not even reach the emission bodies. Replace them with six
DebuggingRecorder tests that enable the gate, pin every metric name the
helpers own, and pin the derived values, branch selection and label
mapping (rustfs/backlog#1836).

* test(tooling): anchor assertless-census delegation tokens to name segments

scripts/find_assertless_tests.py

@@ -28,8 +28,15 @@ called helper. Known false-positive classes are excluded up front:
   parameters; the assert lives in the shared body — still scanned, but a
   body that asserts is not flagged anyway; the exclusion covers wrappers
   that only delegate to a suite runner).
-- Functions whose body calls a helper with `assert`, `verify`, `check`,
-  `expect`, `run_` or `_case` in its name (suite-delegation pattern).
+- Functions whose body calls a helper *named* like a shared check or suite
+  runner: an `assert_`/`verify_`/`check_`/`expect_`/`ensure_`/`run_` prefix,
+  or a `_case`/`_cases`/`_harness`/`_roundtrip` suffix. The name must carry
+  the token as its own leading or trailing segment — matching it anywhere
+  inside the identifier hid whole test bodies behind an unrelated domain
+  call such as `record_get_object_bitrot_verify_duration(..)`.
+- Functions whose body only defines an unused inner `fn _name(..)`: that is
+  the compile-time shape check (exhaustive match, signature pin), where the
+  type system is the assertion.
 
 Usage:
     scripts/find_assertless_tests.py [path ...]     # default: crates rustfs/src
@@ -45,7 +52,11 @@ VERIFY_SIGNALS = re.compile(
     r"assert!|assert_eq!|assert_ne!|debug_assert|panic!\(|\.expect\(|\.unwrap\(|"
     r"unreachable!|matches!\(|insta::|proptest!|\.await\?|\)\?|\?;|should_panic"
 )
-DELEGATION = re.compile(r"\b[a-z0-9_]*(?:assert|verify|check|expect|run_case|_case|harness|round_trip|roundtrip)[a-z0-9_]*\s*\(")
+DELEGATION = re.compile(
+    r"\b(?:assert|verify|check|expect|ensure|run)_[a-z0-9_]*\s*\(|"
+    r"\b[a-z0-9_]+_(?:case|cases|harness|roundtrip|round_trip)\s*\("
+)
+COMPILE_TIME_CHECK = re.compile(r"\bfn\s+_[a-zA-Z0-9_]*\s*(?:<[^>]*>)?\s*\(")
 TEST_ATTR = re.compile(r"#\[(?:tokio::)?test[\](]")
 TEST_CASE_ATTR = re.compile(r"#\[test_case")
 FN_LINE = re.compile(r"^\s*(?:pub\s+)?(?:async\s+)?fn\s+([a-zA-Z0-9_]+)")
@@ -94,7 +105,7 @@ def scan_file(path: Path):
                 break
             k += 1
         text = "\n".join(body)
-        if not VERIFY_SIGNALS.search(text) and not DELEGATION.search(text):
+        if not VERIFY_SIGNALS.search(text) and not DELEGATION.search(text) and not COMPILE_TIME_CHECK.search(text):
             print(f"{path}:{j + 1}: {name}")
         i = k + 1