Introduce StaticType::Variadic for variadic parameters

This commit introduces `StaticType::Variadic` to represent variadic
parameter types in function signatures. This allows for more precise
type checking of functions that accept a variable number of arguments,
such as arithmetic operators.

Previously, variadic functions were handled using `StaticType::Any`,
which was too permissive and could lead to runtime errors. The new
`Variadic` type enforces that all arguments must conform to a specified
inner type.

Changes include:

- Adding `StaticType::Variadic` to `src/ast/types.rs`.
- Updating the type checker to handle `Variadic` types correctly when
  unifying with tuples or single arguments.
- Modifying built-in functions like arithmetic operators to use
  `Variadic` for their parameter types.
- Improving error messages for function call mismatches to be more
  specific.
- Adding a new test case to ensure arithmetic type mismatches are caught
  at compile time.
- A new example `data_stream_pipe_buffered.myc` is added.
- The `HMA.myc` example now has a `Skip: output` directive.

tests/rtl.rs

@@ -137,3 +137,17 @@ fn test_environments_from_shared_rtl_are_independent() {
     assert_eq!(format!("{}", env1.run_script("(+ 1 2)").unwrap()), "3");
     assert_eq!(format!("{}", env2.run_script("(+ 1 2)").unwrap()), "3");
 }
+
+/// Arithmetic operators with incompatible types (e.g. Float - Record)
+/// must be caught at compile time, not silently return Void at runtime.
+#[test]
+fn test_arithmetic_type_mismatch_is_compile_error() {
+    let env = Environment::new();
+
+    // Float - Record must fail
+    let res = env.run_script("(do (def r {:price 42.0}) (- 10.0 r))");
+    assert!(
+        res.is_err(),
+        "Float - Record should be a compile error, not silently return Void"
+    );
+}