Reduce Binary sizes

There are a lot of things we can do in the longer term to help this. We can split out the crates into multiple separate crates like psbt, interpreter, descriptor and policy. This would reduce the compilation time and memory usage by offering flexibility.

As pointed by benma , this is because we use a lot of generics. In particular, almost every single function is being monomorphized for each Ctx.
There are 4 types of Contexts (Bare, Legacyp2sh, Segwitv0, Taproot) that are compiled for each descriptor method. One idea might be to define Terminal without the Context. Guard Miniscript with appropriate Context while in the constructor Miniscript::from_ast. This should significantly reduce the code duplication and have a good impact on binary sizes.

Originally posted by @sanket1729 in https://github.com/rust-bitcoin/rust-miniscript/issues/584#issuecomment-1657796630

Review the crate layout and the Context, Terminal, and Miniscript::from_ast areas named in the issue. Establish a reproducible binary-size comparison before choosing between crate splitting and reducing Context-driven monomorphization; done means a measured reduction, but the issue does not specify a target or test.