Unified Stream trait: read() and write() on one type

Stream trait: read() returns PesFrame, write() accepts PesFrame.
A stream is a stream — you read from it or write to it.
No separate Input/Output traits.

API: libfreemkv::input(url) and libfreemkv::output(url, title, codecs)
Returns Box<dyn Stream>.

.github/workflows/ci.yml

@@ -6,6 +6,16 @@ on:
   pull_request:
 
 jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v5
+      - uses: dtolnay/rust-toolchain@1.86.0
+        with:
+          components: clippy, rustfmt
+      - run: cargo fmt --check
+      - run: cargo clippy -- -D warnings
+
   test:
     runs-on: ubuntu-latest
     steps: