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.

src/build_options.rs

@@ -0,0 +1,102 @@
+use crate::package::BuildType;
+use anyhow::Result;
+
+const BUILD_DEPOT_STATIC_OPTION: &str = "BUILD_DEPOT_STATIC";
+
+fn parse_boolish_option(value: &str) -> Option<bool> {
+    match value.trim().to_ascii_lowercase().as_str() {
+        "1" | "true" | "yes" | "on" | "enable" | "enabled" | "static" => Some(true),
+        "0" | "false" | "no" | "off" | "disable" | "disabled" | "shared" => Some(false),
+        _ => None,
+    }
+}
+
+fn normalize_string_option(value: Option<&'static str>) -> Option<String> {
+    value.and_then(|value| {
+        let trimmed = value.trim();
+        (!trimmed.is_empty()).then(|| trimmed.to_string())
+    })
+}
+
+pub(crate) fn requested_static_build() -> Result<Option<bool>> {
+    let Some(raw) = option_env!("BUILD_DEPOT_STATIC") else {
+        return Ok(None);
+    };
+    let raw = raw.trim();
+    if raw.is_empty() {
+        return Ok(None);
+    }
+    parse_boolish_option(raw).ok_or_else(|| {
+        anyhow::anyhow!(
+            "Invalid -D{} value '{}'; expected true/false, on/off, enable/disable, static/shared, or 1/0",
+            BUILD_DEPOT_STATIC_OPTION,
+            raw
+        )
+    }).map(Some)
+}
+
+pub(crate) fn build_tool_package_option(build_type: BuildType) -> Option<&'static str> {
+    match build_type {
+        BuildType::Autotools => Some("DEPOT_AUTOTOOLS_PACKAGE"),
+        BuildType::CMake => Some("DEPOT_CMAKE_PACKAGE"),
+        BuildType::Meson => Some("DEPOT_MESON_PACKAGE"),
+        BuildType::Perl => Some("DEPOT_PERL_PACKAGE"),
+        BuildType::Custom => Some("DEPOT_CUSTOM_PACKAGE"),
+        BuildType::Python => Some("DEPOT_PYTHON_PACKAGE"),
+        BuildType::Rust => Some("DEPOT_RUST_PACKAGE"),
+        BuildType::Makefile => Some("DEPOT_MAKEFILE_PACKAGE"),
+        BuildType::Bin | BuildType::Meta => None,
+    }
+}
+
+pub(crate) fn requested_build_tool_package(build_type: BuildType) -> Option<String> {
+    match build_type {
+        BuildType::Autotools => normalize_string_option(option_env!("DEPOT_AUTOTOOLS_PACKAGE")),
+        BuildType::CMake => normalize_string_option(option_env!("DEPOT_CMAKE_PACKAGE")),
+        BuildType::Meson => normalize_string_option(option_env!("DEPOT_MESON_PACKAGE")),
+        BuildType::Perl => normalize_string_option(option_env!("DEPOT_PERL_PACKAGE")),
+        BuildType::Custom => normalize_string_option(option_env!("DEPOT_CUSTOM_PACKAGE")),
+        BuildType::Python => normalize_string_option(option_env!("DEPOT_PYTHON_PACKAGE")),
+        BuildType::Rust => normalize_string_option(option_env!("DEPOT_RUST_PACKAGE")),
+        BuildType::Makefile => normalize_string_option(option_env!("DEPOT_MAKEFILE_PACKAGE")),
+        BuildType::Bin | BuildType::Meta => None,
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{build_tool_package_option, normalize_string_option, parse_boolish_option};
+    use crate::package::BuildType;
+
+    #[test]
+    fn parse_boolish_option_accepts_expected_values() {
+        assert_eq!(parse_boolish_option("true"), Some(true));
+        assert_eq!(parse_boolish_option("enable"), Some(true));
+        assert_eq!(parse_boolish_option("shared"), Some(false));
+        assert_eq!(parse_boolish_option("off"), Some(false));
+        assert_eq!(parse_boolish_option("maybe"), None);
+    }
+
+    #[test]
+    fn normalize_string_option_trims_and_drops_empty_values() {
+        assert_eq!(
+            normalize_string_option(Some("  meson-bootstrap  ")),
+            Some("meson-bootstrap".to_string())
+        );
+        assert_eq!(normalize_string_option(Some("   ")), None);
+        assert_eq!(normalize_string_option(None), None);
+    }
+
+    #[test]
+    fn build_tool_package_option_maps_supported_builders() {
+        assert_eq!(
+            build_tool_package_option(BuildType::Meson),
+            Some("DEPOT_MESON_PACKAGE")
+        );
+        assert_eq!(
+            build_tool_package_option(BuildType::CMake),
+            Some("DEPOT_CMAKE_PACKAGE")
+        );
+        assert_eq!(build_tool_package_option(BuildType::Bin), None);
+    }
+}