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.lock

@@ -642,6 +642,19 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "chrono"
+version = "0.4.43"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fac4744fb15ae8337dc853fee7fb3f4e48c0fbaa23d0afe49c447b4fab126118"
+dependencies = [
+ "iana-time-zone",
+ "js-sys",
+ "num-traits",
+ "wasm-bindgen",
+ "windows-link 0.2.1",
+]
+
 [[package]]
 name = "clap"
 version = "4.5.59"
@@ -1480,6 +1493,30 @@ version = "0.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "dfa686283ad6dd069f105e5ab091b04c62850d3e4cf5d67debad1933f55023df"
 
+[[package]]
+name = "iana-time-zone"
+version = "0.1.65"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e31bc9ad994ba00e440a8aa5c9ef0ec67d5cb5e5cb0cc7f8b744a35b389cc470"
+dependencies = [
+ "android_system_properties",
+ "core-foundation-sys",
+ "iana-time-zone-haiku",
+ "js-sys",
+ "log",
+ "wasm-bindgen",
+ "windows-core 0.61.2",
+]
+
+[[package]]
+name = "iana-time-zone-haiku"
+version = "0.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f31827a206f56af32e590ba56d5d2d085f558508192593743f16b2306495269f"
+dependencies = [
+ "cc",
+]
+
 [[package]]
 name = "icu_collections"
 version = "2.1.1"
@@ -1841,6 +1878,7 @@ dependencies = [
 name = "myc"
 version = "0.1.0"
 dependencies = [
+ "chrono",
  "clap",
  "eframe",
  "lazy_static",