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!

Cargo.toml

@@ -1,5 +1,5 @@
 [workspace]
-members = ["libconlang", "cl-repl"]
+members = ["libconlang", "cl-repl", "cl-interpret"]
 resolver = "2"
 
 [workspace.package]