Adds two new fuzz harnesses;
- Structured roundtrip.
- Structured reader.
The read/write functionality implementation level is
not symmetrical and some functions plugins e.g.
zipcrypt is only supported for decompressing. Hence
why we need both a "roundtrip" and a reader harness.
Adds a seed-corpus for;
- The existing from_zip harness.
- The new structured reader harness.
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Signed-off-by: Nathaniel Brough <nathaniel.brough@gmail.com>