interpreter: Break out into a separate crate

My editor's performance was tanking because of macro interpreter::builtins::builtin!

Temporary solution: move the interpreter into a separate crate

If I intended to keep the interpreter around, in the long-term, it might be an idea to make a proc-macro for builtin expansion.
However, the only reason I need the macros is because the interpreter's dynamic typing implementation is so half-baked. After I bang out the new type checker/inference engine, I'll have to rewrite the entire interpreter anyway!

cl-interpret/Cargo.toml

@@ -0,0 +1,11 @@
+[package]
+name = "cl-interpret"
+repository.workspace = true
+version.workspace = true
+authors.workspace = true
+edition.workspace = true
+license.workspace = true
+publish.workspace = true
+
+[dependencies]
+conlang = { path = "../libconlang" }