Owned pixel buffer for no-copy presentation

This is based on the API that will be used for no-copy presentation. But
wraps it in `set_buffer`.

This also fixes the Wayland buffer code to set `self.width` and
`self.height` on resize, and set the length of the shared memory file
when the buffer is created.

Co-authored-by: jtnunley <jtnunley01@gmail.com>

.github/workflows/ci.yml

@@ -17,6 +17,17 @@ jobs:
     - name: Check Formatting
       run: cargo +stable fmt --all -- --check
 
+  miri-tests:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - uses: hecrj/setup-rust-action@v1
+      with:
+        rust-version: nightly
+        components: miri
+    - name: Run tests with miri
+      run: cargo +nightly miri test
+
   tests:
     name: Tests
     strategy: