Fuzz testing

tfm crate

From the root of the repository:

cargo fuzz run --fuzz-dir crates/tfm/fuzz --dev fuzz_tftopl

The --dev flag may be optional, but on my computer it results in linker errors.

If a failing input is found and Texcraft does not panic, the fuzzing harness will automatically add data for a test case to crates/tfm/bin/tests/data. A new test can then be added in convert.rs.

In the case when Texcraft panics (or in general), run the fuzzer with TEXCRAFT_FUZZ_OUTPUT_ALWAYS=1 to always write test cases out.