feat: Implement platform-specific hosts file path retrieval

- Created a new `platform` package to handle OS-specific hosts file paths.
- Added implementations for macOS, Linux, and Windows to retrieve the hosts file path.
- Introduced tests for the `GetHostsFilePath` function to ensure correct behavior across platforms.

feat: Add DNS resolver for IP lookups

- Implemented a `resolver` package for performing DNS lookups.
- Created a `DNSResolver` struct with a `LookupIP` method to handle A-record lookups and CNAME resolution.
- Added comprehensive tests for various DNS scenarios, including CNAME chains and error handling.

chore: Refactor project structure and update dependencies

- Restructured the project to follow Go's standard package layout.
- Updated `go.mod` to Go 1.20 and added `golang.org/x/net` dependency.
- Removed old source files and ensured a clean build with all tests passing.

platform/platform_darwin.go

@@ -0,0 +1,21 @@
+//go:build darwin
+
+package platform
+
+import (
+	"fmt"
+	"os"
+)
+
+// GetHostsFilePath returns the absolute path to the system hosts file on macOS.
+// Returns an error if the file does not exist or cannot be accessed.
+func GetHostsFilePath() (string, error) {
+	path := "/etc/hosts"
+	if _, err := os.Stat(path); err != nil {
+		if os.IsNotExist(err) {
+			return "", fmt.Errorf("file does not exist: %s", path)
+		}
+		return "", fmt.Errorf("accessing hosts file: %w", err)
+	}
+	return path, nil
+}