Add from_str to Script

[riverKanies]

would be nice to be able to create a Script from a string

context: just implemented as_bytes on bdk-wasm ScriptBuf since it only had toString, wouldn't hurt to have to/from string here

[thunderbiscuit]

Here do you mean a hex string? If so it would just be a matter of exposing this method.

[riverKanies]

Iirc it was from human readable string that was useful while implementing payjoin.

This is probably better to revisit when someone actually implements payjoin using bdk bindings other than Wasm

Just seemed like a simple intuitively useful addition (if I have a human readable script string should't I be able to construct a bdk::Script with it?)