refactor(api): restructured API for type safety, maintainability and docs generation

- These changes makes the API incombatible with previous versions
- Added new types for error handling, success responses, and health checks.
- Updated health check logic to utilize the new types for better clarity and structure.
- Refactored existing handlers to improve response consistency and error handling.
- Updated Makefile to include a new target for generating API types from Swagger.
- Updated "new agent" API to respond an encrypted cert pair

internal/net/gphttp/loadbalancer/round_robin.go

@@ -3,17 +3,19 @@ package loadbalancer
 import (
 	"net/http"
 	"sync/atomic"
+
+	"github.com/yusing/go-proxy/internal/types"
 )
 
 type roundRobin struct {
 	index atomic.Uint32
 }
 
-func (*LoadBalancer) newRoundRobin() impl        { return &roundRobin{} }
-func (lb *roundRobin) OnAddServer(srv Server)    {}
-func (lb *roundRobin) OnRemoveServer(srv Server) {}
+func (*LoadBalancer) newRoundRobin() impl                          { return &roundRobin{} }
+func (lb *roundRobin) OnAddServer(srv types.LoadBalancerServer)    {}
+func (lb *roundRobin) OnRemoveServer(srv types.LoadBalancerServer) {}
 
-func (lb *roundRobin) ServeHTTP(srvs Servers, rw http.ResponseWriter, r *http.Request) {
+func (lb *roundRobin) ServeHTTP(srvs types.LoadBalancerServers, rw http.ResponseWriter, r *http.Request) {
 	index := lb.index.Add(1) % uint32(len(srvs))
 	srvs[index].ServeHTTP(rw, r)
 	if lb.index.Load() >= 2*uint32(len(srvs)) {