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/records.rs

@@ -100,12 +100,12 @@ fn test_record_errors() {
     // 1. Missing field
     let res_missing = env.run_script("(.missing {:a 1})");
     assert!(res_missing.is_err());
-    assert!(res_missing.unwrap_err().contains("Invalid arguments"));
+    assert!(res_missing.unwrap_err().contains("no matching overload"));
 
     // 2. Not a record
     let res_not_rec = env.run_script("(.name 123)");
     assert!(res_not_rec.is_err());
-    assert!(res_not_rec.unwrap_err().contains("Invalid arguments"));
+    assert!(res_not_rec.unwrap_err().contains("no matching overload"));
 }
 
 #[test]