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.

examples/closure.myc

@@ -0,0 +1,10 @@
+;; Closure Scope Test
+;; Output: 15
+(do
+  (def make-adder (fn [x] 
+    (fn [y] (+ x y))))
+
+  (def add5 (make-adder 5))
+  
+  (add5 10)
+)

examples/fib.myc

@@ -0,0 +1,10 @@
+;; Fibonacci Recursive
+;; Output: 55
+(do
+  (def fib (fn [n]
+    (if (< n 2)
+      n
+      (+ (fib (- n 1)) (fib (- n 2))))))
+
+  (fib 10)
+)

examples/hof.myc

@@ -0,0 +1,8 @@
+;; Higher-Order Function Example
+;; Output: 25
+(do
+  (def apply (fn [f x] (f x)))
+  (def square (fn [x] (* x x)))
+
+  (apply square 5)
+)