feat: replace log with rs/zerolog for structured logging

Switch from the standard library log package to rs/zerolog with
ConsoleWriter for colorful terminal output in dev mode and JSON
output in production. Users can now provide their own logger via
Options.Logger or set the level via Options.LogLevel.

context.go

@@ -5,7 +5,6 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
-	"log"
 	"maps"
 	"reflect"
 	"sync"
@@ -456,7 +455,7 @@ func (c *Context) unsubscribeAll() {
 
 func newContext(id string, route string, v *V) *Context {
 	if v == nil {
-		log.Fatal("create context failed: app pointer is nil")
+		panic("create context failed: app pointer is nil")
 	}
 
 	return &Context{