feat: Add lambda collection and specialization

Introduces `LambdaCollector` to gather lambda functions and populate the
function registry. This enables the `Specializer` to work with
user-defined functions.

The `Environment` struct is updated to manage the `function_registry`
and `monomorph_cache`, which are essential for the specialization
process.

The `link` method in `Environment` now incorporates lambda collection
and node specialization before applying TCO optimization. This ensures
that lambdas are properly processed and specialized for potential
performance gains.

The `Specializer`'s `new` constructor has been modified to accept and
initialize the `MonoCache` through an `Rc<RefCell<MonoCache>>`. This
allows the cache to be shared across different specialized functions.

Also includes minor refactoring and type adjustments in `specializer.rs`
for better clarity and consistency.

src/ast/rtl/mod.rs

@@ -1,6 +1,7 @@
 pub mod core;
 pub mod datetime;
 pub mod type_registry;
+pub mod intrinsics;
 
 use crate::ast::environment::Environment;