docs: add comprehensive package documentation for rulematcher

- Add detailed package documentation to engine.go explaining the rule matching
  system, supported rule types (Network, MAC, Domain), and priority ordering
- Include usage example demonstrating typical API usage patterns
- Remove unused Type() method from RuleMatcher interface and implementations
- Maintain backward compatibility while improving code documentation

The documentation explains the policy-based DNS routing system and how different
rule types interact with configurable priority ordering.

config.go

@@ -317,7 +317,7 @@ func (lc *ListenerConfig) IsDirectDnsListener() bool {
 
 // MatchingConfig defines the configuration for rule matching behavior
 type MatchingConfig struct {
-	Order []string `mapstructure:"order" toml:"order,omitempty" json:"order" yaml:"order"`
+	Order []string `mapstructure:"order" toml:"order,omitempty"`
 }
 
 // ListenerPolicyConfig specifies the policy rules for ctrld to filter incoming requests.