[core] fast_select scan removal: address review feedback

- Drop redundant cached_sock_ = nullptr assignment in close(). After
  closed_ = true the socket is a corpse and no ready() or other member
  access is valid, so the nulling is not load-bearing. The comment now
  explains why on both impl variants.

- Reword the yield_with_select_ comment so the wake-source sentence
  reads as a complete list rather than a trailing fragment.

esphome/components/socket/bsd_sockets_impl.cpp

@@ -34,11 +34,10 @@ BSDSocketImpl::~BSDSocketImpl() {
 
 int BSDSocketImpl::close() {
   if (!this->closed_) {
-#ifdef USE_LWIP_FAST_SELECT
-    // All LwIP sockets share the same static event_callback, so there is no per-socket
-    // unhook needed — just drop the cached pointer before the socket is destroyed.
-    this->cached_sock_ = nullptr;
-#else
+#ifndef USE_LWIP_FAST_SELECT
+    // All LwIP sockets share the same static event_callback, so on the fast-select path
+    // there is no per-socket unhook needed. cached_sock_ is not cleared because closed_
+    // makes the socket a corpse — no ready() or other member access is valid afterwards.
     if (this->loop_monitored_) {
       App.unregister_socket_fd(this->fd_);
     }

esphome/components/socket/lwip_sockets_impl.cpp

@@ -34,11 +34,10 @@ LwIPSocketImpl::~LwIPSocketImpl() {
 
 int LwIPSocketImpl::close() {
   if (!this->closed_) {
-#ifdef USE_LWIP_FAST_SELECT
-    // All LwIP sockets share the same static event_callback, so there is no per-socket
-    // unhook needed — just drop the cached pointer before the socket is destroyed.
-    this->cached_sock_ = nullptr;
-#else
+#ifndef USE_LWIP_FAST_SELECT
+    // All LwIP sockets share the same static event_callback, so on the fast-select path
+    // there is no per-socket unhook needed. cached_sock_ is not cleared because closed_
+    // makes the socket a corpse — no ready() or other member access is valid afterwards.
     if (this->loop_monitored_) {
       App.unregister_socket_fd(this->fd_);
     }

esphome/core/application.h

@@ -895,8 +895,8 @@ inline void ESPHOME_ALWAYS_INLINE Application::yield_with_select_(uint32_t delay
   // event_callback wrapper (see lwip_fast_select.c) are the single source of truth for
   // socket wake-ups. Every NETCONN_EVT_RCVPLUS posts an xTaskNotifyGive, so any notification
   // that lands between wakes keeps the counter non-zero (next ulTaskNotifyTake returns
-  // immediately) or wakes a blocked Take directly. Also woken by wake_loop_threadsafe()
-  // from background tasks, or timeout.
+  // immediately) or wakes a blocked Take directly. Additional wake sources:
+  // wake_loop_threadsafe() from background tasks, and the delay_ms timeout.
   if (delay_ms == 0) [[unlikely]] {
     yield();
     return;