fix: use rust-embed for DSL files

[kevaundray]

Problem

env! is evaluated at build time, so for example if we compile the crate into static libraries, the path to the DSL files will be hardcoded into the binary. This will be something like /user/tom/leanMultiSig/main.py. This is usually okay for local development, however when we want to package this so that we can use it in Python, the path will be fetched at runtime.

Potential solutions

There are two solutions that I know of for solving this:

• explicitly pass the path to main.py in as a parameter when compiling main
• ensure that even after compiling, we have a valid path to the main.py file

This PR goes with the second option, by embedding the dsl files into the binary with rust-embed and then creating a path to them at runtime when needed. This means that users of this library will not need to worry about supplying a path to the main.py file.