Function expr_to_value 

pub fn expr_to_value(expr: Expr) -> Value

Convert a parsed Expr to a runtime Value.

Handles all structurally representable forms; compile-only forms (lambdas, wasm locals, etc.) that cannot appear in wire output map to Nil. Keywords (:foo) map to Value::Symbol(":foo") to preserve plist key identity.

Depth is bounded to [MAX_VALUE_DEPTH]; call [expr_to_value_depth] directly when a depth budget is already in scope.