feat: RESP3 notifications support & Hitless notifications handling [CAE-1088] & [CAE-1072] (#3418)

- Adds support for handling push notifications with RESP3. 
- Using this support adds handlers for hitless upgrades.

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Hristo Temelski <hristo.temelski@redis.com>

push/handler_context.go

@@ -0,0 +1,44 @@
+package push
+
+// No imports needed for this file
+
+// NotificationHandlerContext provides context information about where a push notification was received.
+// This struct allows handlers to make informed decisions based on the source of the notification
+// with strongly typed access to different client types using concrete types.
+type NotificationHandlerContext struct {
+	// Client is the Redis client instance that received the notification.
+	// It is interface to both allow for future expansion and to avoid
+	// circular dependencies. The developer is responsible for type assertion.
+	// It can be one of the following types:
+	// - *redis.baseClient
+	// - *redis.Client
+	// - *redis.ClusterClient
+	// - *redis.Conn
+	Client interface{}
+
+	// ConnPool is the connection pool from which the connection was obtained.
+	// It is interface to both allow for future expansion and to avoid
+	// circular dependencies. The developer is responsible for type assertion.
+	// It can be one of the following types:
+	// - *pool.ConnPool
+	// - *pool.SingleConnPool
+	// - *pool.StickyConnPool
+	ConnPool interface{}
+
+	// PubSub is the PubSub instance that received the notification.
+	// It is interface to both allow for future expansion and to avoid
+	// circular dependencies. The developer is responsible for type assertion.
+	// It can be one of the following types:
+	// - *redis.PubSub
+	PubSub interface{}
+
+	// Conn is the specific connection on which the notification was received.
+	// It is interface to both allow for future expansion and to avoid
+	// circular dependencies. The developer is responsible for type assertion.
+	// It can be one of the following types:
+	// - *pool.Conn
+	Conn interface{}
+
+	// IsBlocking indicates if the notification was received on a blocking connection.
+	IsBlocking bool
+}