Add 113 tests, update CI to checkout@v5, add FEATURES.md

Test suite: 64 → 177 tests
- MPLS parser: 6 tests (synthetic binary, streams, errors)
- CLPI parser: 6 tests (EP map, PTS/SPN math, errors)
- H.264: 12 tests (NAL parsing, SPS/PPS, keyframes)
- HEVC: 13 tests (VPS/SPS/PPS, IRAP range, codec private)
- AC3: 12 tests (syncword, frame extraction)
- VC1: 15 tests (BITMAPINFOHEADER, start codes)
- DTS: 5, TrueHD: 4, PGS: 4 tests
- EBML: 6 tests (size/ID/string/float roundtrips)
- UDF: 10 tests (MockSectorReader, filesystem parsing, error paths)
- Disc: 8 tests (scan_image, DiscTitle helpers)
- Streams: 5 new (meta roundtrip, MkvStream)
- NullStream: 4, StdioStream: 2, IsoSectorReader: 2

CI: actions/checkout@v4 → v5 (all workflows)
FEATURES.md: created for v0.7.1

.github/workflows/release.yml

@@ -12,7 +12,7 @@ jobs:
   verify:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
       - name: Verify Cargo.toml version matches tag
         run: |
           CARGO_VER="v$(grep '^version' Cargo.toml | head -1 | sed 's/.*"\(.*\)"/\1/')"
@@ -26,7 +26,7 @@ jobs:
     needs: verify
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
       - uses: dtolnay/rust-toolchain@stable
       - run: cargo test
 
@@ -34,7 +34,7 @@ jobs:
     needs: test
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
       - uses: dtolnay/rust-toolchain@stable
       - name: Publish to crates.io
         run: cargo publish
@@ -45,7 +45,7 @@ jobs:
     needs: test
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
       - name: Create GitHub Release
         uses: softprops/action-gh-release@v2
         with: