test: compile the facade's parallel tests, and build them in CI

parallel_integration.rs declared `_sequential` and used `sequential`
under the parallel feature, which nothing in CI enabled for the facade.
ci-test.sh now lints and tests the facade with parallel on.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

crates/clawhdf5/tests/parallel_integration.rs

@@ -292,7 +292,8 @@ mod parallel_tests {
         }
 
         // Sequential decompression
-        let _sequential: Vec<Vec<u8>> = chunk_infos
+        #[cfg_attr(not(feature = "parallel"), allow(unused_variables))]
+        let sequential: Vec<Vec<u8>> = chunk_infos
             .iter()
             .map(|ci| {
                 let addr = ci.address as usize;

scripts/ci-test.sh

@@ -82,11 +82,13 @@ plugin_filters_alone() {
 }
 run_step "cargo clippy (each plugin filter alone)" plugin_filters_alone
 
-# The facade's plugin-filter interop tests only build with the features on.
+# The facade's plugin-filter interop tests and its parallel decoding tests
-run_step "cargo clippy (facade plugin filters)" cargo clippy \
+# only build with those features on (parallel_integration.rs stopped
+# compiling unnoticed while nothing built it).
+run_step "cargo clippy (facade plugin filters + parallel)" cargo clippy \
     -p clawhdf5 \
     --all-targets \
-    --features plugin-filters \
+    --features plugin-filters,parallel \
     -- -D warnings
 
 # The HNSW index's parallel bulk build is feature-gated too.
@@ -180,6 +182,10 @@ run_step "cargo test (format feature matrix)" cargo test \
     -p clawhdf5-format \
     --features parallel,lz4,zstd,pcodec,fast-checksum,plugin-filters
 
+run_step "cargo test (facade parallel)" cargo test \
+    -p clawhdf5 \
+    --features parallel
+
 run_step "cargo test (ann parallel)" cargo test \
     -p clawhdf5-ann \
     --features parallel