Allow any expression as constants

This is only a start. It compiles, but with a few TODOs left open. In particular, it doesn't currently handle constants depending on other constants or functions; nor does it hoist constants.

crates/uplc/src/tx/error.rs

@@ -19,7 +19,7 @@ pub enum Error {
             format!(
                 "\n{:>13} {}",
                 "Trace",
-                if trace.contains("\n") {
+                if trace.contains('\n') {
                     trace.lines()
                         .enumerate()
                         .map(|(ix, row)| {