Miniscript descriptors are defined under P2WSH context (either `wsh()`
or `sh(wsh())`).
Only sane Miniscripts are accepted, as insane ones (although valid by
type) can have surprising behaviour with regard to malleability
guarantees and resources limitations.
As Miniscript descriptors are longer and more complex than "legacy"
descriptors, care was taken in error reporting to help a user determine
for what reason a provided Miniscript is insane.
Co-authored-by: Pieter Wuille <pieter.wuille@gmail.com>
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