Port test data tests to Rust

Currently we're running the test data tests by hacking the Meson test runner to invoke the rav1d Rust executable instead of the dav1d C executable. This is good enough for testing locally and in CI, but it's not ideal for a few reasons:

• Not idiomatic Rust, would be better to use cargo test.
• Doesn't automatically rebuild, you have to remember to run cargo build --release before running tests or they'll run against an out-of-date binary.
• Runs against release builds instead of debug builds, which makes debugging harder.
• We don't want to have to maintain the Meson scripts long term.
• It would also be good to have some examples of invoking rav1d from Rust, and writing Rust tests would be a good way of doing that.

We should port these tests over to the standard Rust test harness so that we can run our test suite with cargo test. Since there are 790 test files, this is probably best done by writing a one-off script to generate a test for each file, along with the correct MD5 checksums.

Start by inspecting the current Meson test-runner setup and the existing test-data files, then run the current cargo test and rav1d test commands to compare behavior. Generate coverage for all 790 files with the correct MD5 checksums, and confirm the suite runs through the standard Rust test harness without requiring the Meson workaround.