Add chrono dependency and example files

This commit introduces the `chrono` dependency to the project, enabling
the use of time-related functionalities. Additionally, it adds several
example files (`closure.myc`, `fib.myc`, `hof.myc`) to showcase the
language's features like closures, recursion, and higher-order
functions.

The `Cargo.lock` and `Cargo.toml` files have been updated to reflect the
new dependency. The `integration_test.rs` file now includes a test to
run all `.myc` files found in the `examples` directory, ensuring their
correctness. The `main.rs` file has also been updated to load and
display these examples in the UI.

Cargo.toml

@@ -2,8 +2,10 @@
 name = "myc"
 version = "0.1.0"
 edition = "2024"
+default-run = "myc"
 
 [dependencies]
 eframe = "0.33.3"
 lazy_static = "1.4.0"
 clap = { version = "4.5", features = ["derive"] }
+chrono = "0.4"