doughlang: symbol interning and AST reparameterization

- intern: Add interners from cl-intern

- ast:
- Break AST into ternimals (AstTypes) and nonterminals (Expr, Pat, Bind, Make, Use)
- Make AST generic over terminals (except operators, for now)

Cargo.toml

@@ -5,4 +5,5 @@ edition = "2024"
 
 [dependencies]
 repline = "*"
+cl-arena = "*"
 unicode-ident = "1.0.12"