exclude cachet's untestable no-logs telemetry blocks from coverage

`record_{debug,info,error}_with_duration` each contain a
`#[cfg(not(any(feature = "logs", test)))]` no-op block that only exists to
silence unused-variable warnings when logging is compiled out. Under
`--no-default-features` these blocks compile only into non-test builds (notably
cachet's examples) and are never executed, so they surfaced as 9 uncovered
lines under anvil's nextest-based coverage (which instruments example binaries;
oxidizer's libtest `cargo llvm-cov` does not, which is why Codecov shows the
file 100%).

Add `#[cfg_attr(coverage_nightly, coverage(off))]` to the three functions (and
enable `feature(coverage_attribute)` at the crate root) so these untestable
discards are not instrumented. cachet goes 99.7% -> 100%.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: martin-kolinek

crates/cachet/src/lib.rs

@@ -1,6 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // Licensed under the MIT License.
 
+#![cfg_attr(coverage_nightly, feature(coverage_attribute))]
 #![cfg_attr(docsrs, feature(doc_cfg))]
 
 //! A composable, multi-tier caching library with stampede protection, background

crates/cachet/src/telemetry/cache.rs

@@ -142,6 +142,11 @@ impl CacheTelemetry {
         not(feature = "logs"),
         expect(clippy::unused_self, reason = "self.logging_enabled is used when logs is enabled")
     )]
+    // The body is a no-op when `logs` is off; under `--no-default-features`
+    // it only compiles into non-test builds (e.g. examples) and is never
+    // exercised, so exclude it from coverage rather than chase an untestable
+    // discard. See telemetry tests for the logs-on path.
+    #[cfg_attr(coverage_nightly, coverage(off))]
     fn record_debug_with_duration(&self, cache_name: CacheName, event: &'static str, duration: Duration) {
         #[cfg(any(feature = "logs", test))]
         if self.logging_enabled {
@@ -161,6 +166,7 @@ impl CacheTelemetry {
         not(feature = "logs"),
         expect(clippy::unused_self, reason = "self.logging_enabled is used when logs is enabled")
     )]
+    #[cfg_attr(coverage_nightly, coverage(off))]
     fn record_info_with_duration(&self, cache_name: CacheName, event: &'static str, duration: Duration) {
         #[cfg(any(feature = "logs", test))]
         if self.logging_enabled {
@@ -180,6 +186,7 @@ impl CacheTelemetry {
         not(feature = "logs"),
         expect(clippy::unused_self, reason = "self.logging_enabled is used when logs is enabled")
     )]
+    #[cfg_attr(coverage_nightly, coverage(off))]
     fn record_error_with_duration(&self, cache_name: CacheName, event: &'static str, duration: Duration) {
         #[cfg(any(feature = "logs", test))]
         if self.logging_enabled {