feat(chrek): external restore, signal-based IPC, and package refactor (#6286)

Co-authored-by: Dan Feigin <dfeigin@nvidia.com>

deploy/chrek/pkg/http_api_server/server.go

-// server.go provides the HTTP server for the checkpoint agent.
-package httpApiServer
-
-import (
-	"context"
-	"log"
-	"net/http"
-	"time"
-
-	"github.com/ai-dynamo/dynamo/deploy/chrek/pkg/checkpoint"
-)
-
-// ServerConfig holds the configuration for the HTTP API server.
-type ServerConfig struct {
-	ListenAddr     string
-	NodeName       string
-	CheckpointSpec *checkpoint.CheckpointSpec
-}
-
-// Server is the HTTP API server for checkpoint operations.
-type Server struct {
-	cfg        ServerConfig
-	handlers   *Handlers
-	httpServer *http.Server
-}
-
-// NewServer creates a new Server instance.
-func NewServer(cfg ServerConfig, checkpointer *checkpoint.Checkpointer) *Server {
-	handlers := NewHandlers(cfg, checkpointer)
-
-	// Setup routes
-	mux := http.NewServeMux()
-	mux.HandleFunc("/health", handlers.HandleHealth)
-	mux.HandleFunc("/checkpoint", handlers.HandleCheckpoint)
-	mux.HandleFunc("/checkpoints", handlers.HandleListCheckpoints)
-
-	// WriteTimeout must exceed the CRIU checkpoint timeout since /checkpoint
-	// blocks until the dump completes. Add 60s buffer for pre/post work.
-	writeTimeout := time.Duration(cfg.CheckpointSpec.CRIU.Timeout)*time.Second + 60*time.Second
-	if writeTimeout < 300*time.Second {
-		writeTimeout = 300 * time.Second
-	}
-
-	httpServer := &http.Server{
-		Addr:         cfg.ListenAddr,
-		Handler:      LoggingMiddleware(mux),
-		ReadTimeout:  30 * time.Second,
-		WriteTimeout: writeTimeout,
-		IdleTimeout:  120 * time.Second,
-	}
-
-	return &Server{
-		cfg:        cfg,
-		handlers:   handlers,
-		httpServer: httpServer,
-	}
-}
-
-// Start starts the HTTP server.
-// This method blocks until the server is shut down.
-func (s *Server) Start() error {
-	log.Printf("HTTP API server listening on %s", s.cfg.ListenAddr)
-	return s.httpServer.ListenAndServe()
-}
-
-// Shutdown gracefully shuts down the server.
-func (s *Server) Shutdown(ctx context.Context) error {
-	log.Println("Shutting down HTTP server...")
-	return s.httpServer.Shutdown(ctx)
-}
-
-// Addr returns the server's listen address.
-func (s *Server) Addr() string {
-	return s.cfg.ListenAddr
-}