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.

hostfile/filesystem.go

@@ -0,0 +1,31 @@
+package hostfile
+
+import "os"
+
+// FileSystem abstracts filesystem operations for testability.
+type FileSystem interface {
+	ReadFile(path string) ([]byte, error)
+	WriteFile(path string, data []byte, perm os.FileMode) error
+	Stat(path string) (os.FileInfo, error)
+	CreateTemp(dir, pattern string) (*os.File, error)
+	Rename(oldpath, newpath string) error
+	Remove(path string) error
+	Chmod(path string, mode os.FileMode) error
+}
+
+// OSFileSystem implements FileSystem using real OS calls.
+type OSFileSystem struct{}
+
+func (OSFileSystem) ReadFile(path string) ([]byte, error) { return os.ReadFile(path) }
+func (OSFileSystem) WriteFile(path string, data []byte, perm os.FileMode) error {
+	return os.WriteFile(path, data, perm)
+}
+func (OSFileSystem) Stat(path string) (os.FileInfo, error) { return os.Stat(path) }
+func (OSFileSystem) CreateTemp(dir, pattern string) (*os.File, error) {
+	return os.CreateTemp(dir, pattern)
+}
+func (OSFileSystem) Rename(oldpath, newpath string) error { return os.Rename(oldpath, newpath) }
+func (OSFileSystem) Remove(path string) error             { return os.Remove(path) }
+func (OSFileSystem) Chmod(path string, mode os.FileMode) error {
+	return os.Chmod(path, mode)
+}