Separate Jet env from Jet trait

[ivanlele]

This PR is one of several that will make the Jet trait object-safe (see #349).
It introduces a new trait, JetEnvironment, which moves c_jet_env, c_jet_ptr, and CJetEnvironment into it from Jet.

[ivanlele]

It might look large, but most of the changes are in the auto-generated jet implementations and consist mainly of formatting and moving code around. This also raises a question: should we update the Haskell-Rust codegen for these implementations now, or leave it for later?

The other changes are relatively few, but nonetheless far more important.

[ivanlele]

Also, while updating interfaces in some files, I ran cargo fmt on the files I was modifying, so you might notice a few lines that were reformatted as a result.

[apoelstra]

This also raises a question: should we update the Haskell-Rust codegen for these implementations now, or leave it for later?

Yes. My local test system will not allow merging code if the autogenerated files differ from what's committed here.

We will need to update the Haskell-Rust codegen first and then PR here to update the vendored version of libsimplicity.

[apoelstra]

In 273d347:

Also, this commit includes a massive amount of formatting changes to files that are autogenerated and have #[rustfmt::skip] on them.