[api] Skip state_action_() call in noise data path

The noise frame helper was calling state_action_() (447 bytes) on every
read_packet() and write_protobuf_messages() call. In the DATA state
(steady-state after handshake), this function falls through all handshake
checks and returns OK — pure overhead on every encrypted packet.

Add check_data_state_() inline helper that replaces the call with a
single byte-load + branch instruction in the hot path. The handshake
state machine continues to be driven by loop() as before.

Also applies consistent state checking to the plaintext frame helper.

esphome/components/api/api_frame_helper.h

@@ -232,6 +232,17 @@ class APIFrameHelper {
     EXPLICIT_REJECT = 8,  // Noise only
   };
 
+  // Fast inline check for read_packet/write_protobuf_messages hot path.
+  // In DATA state, state_action_() is a no-op (falls through all checks to return OK).
+  // This avoids a 447-byte function call on every packet during normal operation.
+  inline APIError ESPHOME_ALWAYS_INLINE check_data_state_() const {
+    if (state_ == State::DATA)
+      return APIError::OK;
+    if (state_ == State::CLOSED || state_ == State::FAILED)
+      return APIError::BAD_STATE;
+    return APIError::WOULD_BLOCK;
+  }
+
   // Containers (size varies, but typically 12+ bytes on 32-bit)
   std::array<std::unique_ptr<SendBuffer>, API_MAX_SEND_QUEUE> tx_buf_;
   std::vector<uint8_t> rx_buf_;

esphome/components/api/api_frame_helper_noise.cpp

@@ -397,14 +397,9 @@ void APINoiseFrameHelper::send_explicit_handshake_reject_(const LogString *reaso
   state_ = orig_state;
 }
 APIError APINoiseFrameHelper::read_packet(ReadPacketBuffer *buffer) {
-  APIError aerr = this->state_action_();
-  if (aerr != APIError::OK) {
+  APIError aerr = this->check_data_state_();
+  if (aerr != APIError::OK)
     return aerr;
-  }
-
-  if (this->state_ != State::DATA) {
-    return APIError::WOULD_BLOCK;
-  }
 
   aerr = this->try_read_frame_();
   if (aerr != APIError::OK)
@@ -461,14 +456,9 @@ APIError APINoiseFrameHelper::write_protobuf_packet(uint8_t type, ProtoWriteBuff
 }
 
 APIError APINoiseFrameHelper::write_protobuf_messages(ProtoWriteBuffer buffer, std::span<const MessageInfo> messages) {
-  APIError aerr = state_action_();
-  if (aerr != APIError::OK) {
+  APIError aerr = this->check_data_state_();
+  if (aerr != APIError::OK)
     return aerr;
-  }
-
-  if (state_ != State::DATA) {
-    return APIError::WOULD_BLOCK;
-  }
 
   if (messages.empty()) {
     return APIError::OK;

esphome/components/api/api_frame_helper_plaintext.cpp

@@ -195,11 +195,11 @@ APIError APIPlaintextFrameHelper::try_read_frame_() {
 }
 
 APIError APIPlaintextFrameHelper::read_packet(ReadPacketBuffer *buffer) {
-  if (this->state_ != State::DATA) {
-    return APIError::WOULD_BLOCK;
-  }
+  APIError aerr = this->check_data_state_();
+  if (aerr != APIError::OK)
+    return aerr;
 
-  APIError aerr = this->try_read_frame_();
+  aerr = this->try_read_frame_();
   if (aerr != APIError::OK) {
     if (aerr == APIError::BAD_INDICATOR) {
       // Make sure to tell the remote that we don't
@@ -244,9 +244,9 @@ APIError APIPlaintextFrameHelper::write_protobuf_packet(uint8_t type, ProtoWrite
 
 APIError APIPlaintextFrameHelper::write_protobuf_messages(ProtoWriteBuffer buffer,
                                                           std::span<const MessageInfo> messages) {
-  if (state_ != State::DATA) {
-    return APIError::BAD_STATE;
-  }
+  APIError aerr = this->check_data_state_();
+  if (aerr != APIError::OK)
+    return aerr;
 
   if (messages.empty()) {
     return APIError::OK;