internal/fuzz: handle unrecoverable errors during minimization
Previously, if an unrecoverable error occurred during
minimization, then the input that caused the failure
could not be retrieved by the coordinator. This was fine
if minimizing a crash, since the coordinator could simply
report the original error, and ignore the new one.
However, if an error occurred while minimizing an
interesting input, then we may lose an important error
that would be better to report.
This changes is a pretty major refactor of the minimization
logic in order to support this. It removes minimization
support of all types except []byte and string. There isn't
compelling evidence that minimizing types like int or float64
are actually beneficial, so removing this seems fine.
With this change, the coordinator requests that the worker
minimize a single value at a time. The worker updates shared
memory directly during minimzation, writing the *unmarshaled*
bytes to the shared memory region. If a nonrecoverable error occurs
during minimization, then the coordinator can get the
unmarshaled value out of shared memory for that type being
minimized.