[esphome.ota] Use existing esphome_lwip_get_sock() instead of adding Socket accessor

get_cached_sock() was a new public method that only OTA's fast-select wake
filter would ever call. Drop it. The existing public C API already covers
this: esphome_lwip_get_sock(fd) looks up a lwip_sock* from a file descriptor
(it's exactly what BSDSocketImpl's own constructor calls to populate
cached_sock_). OTA uses the public get_fd() + esphome_lwip_get_sock() chain
instead — no new Socket accessor, no friend declarations, no layering
concerns. The one-time lookup at setup is negligible.

esphome/components/esphome/ota/ota_esphome.cpp

@@ -78,7 +78,9 @@ void ESPHomeOTAComponent::setup() {
   // every RCVPLUS across all monitored sockets (API client data, mDNS, etc.) would
   // pay the inline hook's two volatile stores + memw barriers to mark OTA
   // pending-enable, even though OTA would just re-disable itself on the next tick.
-  esphome_fast_select_set_ota_listener_sock(this->server_->get_cached_sock());
+  // Uses the existing public esphome_lwip_get_sock() lookup instead of adding a
+  // dedicated accessor on Socket — the lookup happens once at setup, not per event.
+  esphome_fast_select_set_ota_listener_sock(esphome_lwip_get_sock(this->server_->get_fd()));
 #endif
 }
 

esphome/components/socket/bsd_sockets_impl.h

@@ -118,15 +118,6 @@ class BSDSocketImpl {
 
   int get_fd() const { return this->fd_; }
 
-#ifdef USE_LWIP_FAST_SELECT
-  // Cached lwip_sock pointer captured at construction. Used by OTA to register its
-  // listener netconn with the fast-select wake hook filter so the hook only fires on
-  // OTA-relevant events. Returns nullptr for non-monitored sockets.
-  struct lwip_sock *get_cached_sock() const {
-    return this->cached_sock_;
-  }
-#endif
-
  protected:
   int fd_{-1};
 #ifdef USE_LWIP_FAST_SELECT

esphome/components/socket/lwip_sockets_impl.h

@@ -84,13 +84,6 @@ class LwIPSocketImpl {
 
   int get_fd() const { return this->fd_; }
 
-#ifdef USE_LWIP_FAST_SELECT
-  // See BSDSocketImpl::get_cached_sock() — same purpose, same semantics.
-  struct lwip_sock *get_cached_sock() const {
-    return this->cached_sock_;
-  }
-#endif
-
  protected:
   int fd_{-1};
 #ifdef USE_LWIP_FAST_SELECT