fix(asynch): replace runtime panic with compile_error for async-std-rt deprecation

async-std has been discontinued (RUSTSEC-2025-0052). Using panic!() inside a
#[cfg(feature = "async-std-rt")] block caused clippy to report an unreachable
statement on the subsequent futures-rt block when --all-features was used, because
panic!() is a diverging expression.

Replace the runtime panic with a module-level compile_error!() so:
- Users get a clear compile-time message instead of a runtime panic
- No unreachable-code lint is triggered (compile_error! is at module level)
- The CI clippy step now uses an explicit feature list excluding async-std-rt
  (--all-features would always fail since compile_error! fires unconditionally)

Author: e-desouza

.github/workflows/build_and_lint.yml

@@ -34,7 +34,9 @@ jobs:
         run: cargo fmt --all -- --check
 
       - name: Clippy
-        run: cargo clippy --all-features -- -D warnings
+        # Exclude async-std-rt: it is deprecated (RUSTSEC-2025-0052) and emits a
+        # compile_error! at crate level, so --all-features would always fail.
+        run: cargo clippy --features std,tokio-rt,embassy-rt,actix-rt,futures-rt,smol-rt,core,wallet,models,utils,helpers,json-rpc,websocket,cli -- -D warnings
 
       - name: Build (default)
         run: cargo build --release

src/asynch/mod.rs

@@ -11,6 +11,16 @@ pub mod transaction;
 #[cfg(feature = "helpers")]
 pub mod wallet;
 
+// async-std has been discontinued (RUSTSEC-2025-0052). Emit a compile-time error so
+// callers get a clear message instead of a runtime panic, and avoid unreachable-code
+// lint when --all-features is used alongside other runtime feature flags.
+#[cfg(feature = "async-std-rt")]
+compile_error!(
+    "The async-std-rt feature is deprecated and no longer supported. \
+     async-std has been discontinued (RUSTSEC-2025-0052). \
+     Use the smol-rt feature instead."
+);
+
 async fn wait_seconds(_seconds: u64) {
     #[cfg(feature = "tokio-rt")]
     {
@@ -25,20 +35,6 @@ async fn wait_seconds(_seconds: u64) {
         use core::time::Duration;
         actix_rt::time::sleep(Duration::from_secs(_seconds)).await;
     }
-    #[cfg(feature = "async-std-rt")]
-    {
-        #[deprecated(
-            since = "1.1.0",
-            note = "async-std has been discontinued (RUSTSEC-2025-0052). Use the smol-rt feature instead."
-        )]
-        fn async_std_sleep_deprecated() {}
-        #[allow(deprecated)]
-        async_std_sleep_deprecated();
-        panic!(
-            "The async-std-rt feature is deprecated. async-std has been discontinued \
-             (RUSTSEC-2025-0052). Use the smol-rt feature instead."
-        );
-    }
     #[cfg(feature = "futures-rt")]
     {
         use core::time::Duration;