Implement update check functionality with version comparison and archive listing

- Added `check.rs` to handle package update checks, including logic for determining available updates from remote git repositories and archive listings.
- Introduced `versions.rs` to manage version patterns, comparison logic, and extraction of candidate versions from git refs and archive listings.
- Implemented `hex.rs` for encoding byte arrays to lowercase hexadecimal strings.

build.rs

@@ -0,0 +1,20 @@
+const BUILD_OPTION_KEYS: &[&str] = &[
+    "BUILD_DEPOT_STATIC",
+    "DEPOT_AUTOTOOLS_PACKAGE",
+    "DEPOT_CMAKE_PACKAGE",
+    "DEPOT_MESON_PACKAGE",
+    "DEPOT_PERL_PACKAGE",
+    "DEPOT_CUSTOM_PACKAGE",
+    "DEPOT_PYTHON_PACKAGE",
+    "DEPOT_RUST_PACKAGE",
+    "DEPOT_MAKEFILE_PACKAGE",
+];
+
+fn main() {
+    for key in BUILD_OPTION_KEYS {
+        println!("cargo:rerun-if-env-changed={key}");
+        if let Ok(value) = std::env::var(key) {
+            println!("cargo:rustc-env={key}={value}");
+        }
+    }
+}