Basic Rust workflow for both crates (#35)

further improvements would be
* code coverage
* skipping changes that doesn't touch that two crates

.github/workflows/rust.yml

@@ -0,0 +1,14 @@
+name: Rust test suite
+on: [push, pull_request]
+
+jobs:
+  test:
+    name: cargo test
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@nightly
+      - run: cargo test --all-features
+        working-directory: ./rust-k256
+      - run: cargo test --all-features
+        working-directory: ./rust-arkworks