Exclude fuzzing/test data from the published crates.io package

[weiznich]

During a dependency review I noticed that regex-automata includes binary fuzzing and test data. These files are not required for building regex-automata as dependency and make it a hard to review the code. This is similar to https://github.com/rust-lang/regex/pull/1281

This commit introduces a include directive in the Cargo.toml file to explicitly include only those files required to build regex-automata. This excludes the test directory and also reduces the size of the published crate from 122 files, 2.6MiB (610.6KiB compressed) to 77 files, 2.5MiB (584.0KiB compressed) which results in a 150 GB/month traffic reduction for crates.io assuming the current 6 million/month downloads and the difference in the compressed package size.