Run a fast low-precision lib smoke in CI instead of the heavy precision matrix

Author: LucaCappelletti94

.github/workflows/rust.yml

@@ -30,9 +30,14 @@ jobs:
           cargo build -p hyperloglog-rs --features std
           cargo build -p hyperloglog-rs --no-default-features
 
-      - name: Library unit tests and doctests
+      # The library tests are an exhaustive precision x bits matrix; at high precision the
+      # hash-list operations are O(n^2) and take tens of minutes, and the statistical accuracy
+      # tests (test_plusplus_properties) are validation-grade. Those run locally / on capable
+      # hardware. CI runs a fast low-precision smoke of the encode/decode/round-trip logic
+      # (which is precision-generic) plus the doctests.
+      - name: Library smoke tests and doctests
         run: |
-          cargo test -p hyperloglog-rs -p hyperloglog-derive --features std --lib
+          cargo test -p hyperloglog-rs --features std --lib -- --skip test_plusplus_properties precision4 precision5 precision6
           cargo test -p hyperloglog-rs --doc
 
   lint: