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/domain.go

@@ -7,11 +7,6 @@ import (
 // DomainRuleMatcher handles matching of domain-based rules
 type DomainRuleMatcher struct{}
 
-// Type returns the rule type for domain matcher
-func (d *DomainRuleMatcher) Type() RuleType {
-	return RuleTypeDomain
-}
-
 // Match evaluates domain rules against the requested domain
 func (d *DomainRuleMatcher) Match(ctx context.Context, req *MatchRequest) *MatchResult {
 	if req.Policy == nil || len(req.Policy.Rules) == 0 {