fuzz test archive round trip and reading

[niklasf]

This adds a fuzz target to be run via cargo +nightly fuzz run roundtrip.

Currently the archive builder does not have a strategy to handle invalid inputs, so I have manually excluded them for now and marked them with TODO. For example, values that are too large could be rejected by the builder, or simply truncated like the command line ar tool does (#29).

Even so, the fuzzer very quickly finds round trip errors. Example invocation:

$ cargo +nightly fuzz run roundtrip
SUMMARY: libFuzzer: deadly signal
[...]
$ cargo +nightly fuzz tmin roundtrip artifacts/roundtrip/crash-ac1fb9c71264dadbf7b173c19df553a58ade3a5d
[...]
thread 'roundtrip' panicked at fuzz_targets/roundtrip.rs:104:25:
read entry: unexpected EOF in the middle of archive entry header with Model { [...], data: [97, 97], [...] }
[...]

Update: That was due to long identifiers. Now appears to be a working a working baseline.

[mdsteele]

Thanks, this would be great to have. Looks like the lint error was preexisting; if you sync the latest changes it should be fixed now.

[niklasf]

Rebased.

Also added coverage for the GNU builder and reading arbitrary bytes.

[mdsteele]

Thanks!