fuzz: compare scripts from `Expand` and `ExpandFromCache`

[brunoerg]

When testing a descriptor, if it was able to Expand, ExpandFromCache should also work and scripts should be the same. This PR covers it in TestDescriptor for descriptor_parse fuzz.

[DrahtBot]

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[brunoerg]

Rebased

[fanquake]

cc @achow101

[brunoerg]

Closing for now.