test(fuzz): Make cargo fuzz fmt fuzz_write output more reliably equivalent to the code path it follows

[Pr0methean]

This will make it possible to copy and paste the output of cargo fuzz fmt fuzz_write into a unit test with only the following changes:

• Add the test function declaration and the final return of Ok(()).
• Remove zopfli_buffer_size and add ..Default::default() to FullFileOptions instances, unless the test case depends on Zopfli.
• Add all the feature flags the test case depends on.
• Add use statements (with function scope if they're gated on feature flags).
• Run cargo fmt --all.