[WIP] Add xUnit test to decode vp80-00-comprehensive-001.ivf from TestVectors directory

[Copilot]

Thanks for asking me to work on this. I will get started on it and keep this PR's description up to date as I form a plan and make progress.

Original description:

Add a unit test to decode the first available VP8 test vector file (vp80-00-comprehensive-001.ivf) from the TestVectors directory, located at test/VP8.Net.TestVectors/TestVectors/vp80-00-comprehensive-001.ivf. The new test should:

• Be placed in the test/VP8.Net.TestVectors project.
• Use xUnit for the test framework.
• Attempt to load and decode vp80-00-comprehensive-001.ivf from the TestVectors directory.
• Assert that the decoding was successful (e.g., no exceptions thrown, frame count > 0, or similar success criteria).
• Add any supporting code needed to read IVF files if not already present.
• Reference the test vector file with a relative path.
• Name the test appropriately, e.g., DecodeFirstComprehensiveTestVector_Succeeds.
• Include comments and follow the code style of the existing test code.

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