Add Metadata::build_time() method

Adds a convenience method to convert the build_epoch Unix timestamp
to a SystemTime, matching the Go v2 library's BuildTime() method.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: oschwald

CHANGELOG.md

@@ -45,6 +45,7 @@
 - `decode_path()` errors now include path context showing where navigation failed
   (e.g., `path: /city/names/0`), making it easier to debug issues with nested data.
 - `Metadata` and `WithinOptions` now implement `PartialEq` and `Eq` traits.
+- Added `Metadata::build_time()` method to convert `build_epoch` to `SystemTime`.
 - Added `verify()` method for comprehensive database validation. Validates
   metadata, search tree structure, data section separator, and data records.
   Useful for validating database files after download or generation.

src/metadata.rs

@@ -26,3 +26,23 @@ pub struct Metadata {
     /// Size of each record in bits (24, 28, or 32).
     pub record_size: u16,
 }
+
+impl Metadata {
+    /// Returns the database build time as a `SystemTime`.
+    ///
+    /// This converts the `build_epoch` Unix timestamp to a `SystemTime`.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use maxminddb::Reader;
+    ///
+    /// let reader = Reader::open_readfile("test-data/test-data/GeoIP2-City-Test.mmdb").unwrap();
+    /// let build_time = reader.metadata.build_time();
+    /// println!("Database built: {:?}", build_time);
+    /// ```
+    #[must_use]
+    pub fn build_time(&self) -> std::time::SystemTime {
+        std::time::UNIX_EPOCH + std::time::Duration::from_secs(self.build_epoch)
+    }
+}