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.

internal/rulematcher/network.go

@@ -8,11 +8,6 @@ import (
 // NetworkRuleMatcher handles matching of network-based rules
 type NetworkRuleMatcher struct{}
 
-// Type returns the rule type for network matcher
-func (n *NetworkRuleMatcher) Type() RuleType {
-	return RuleTypeNetwork
-}
-
 // Match evaluates network rules against the source IP address
 func (n *NetworkRuleMatcher) Match(ctx context.Context, req *MatchRequest) *MatchResult {
 	if req.Policy == nil || len(req.Policy.Networks) == 0 {