[api] Optimize protobuf varint encoding for flash savings

esphome/components/api/proto.h

@@ -221,7 +221,8 @@ class ProtoWriteBuffer {
   void write(uint8_t value) { this->buffer_->push_back(value); }
 
   // Single implementation that all overloads delegate to
-  void encode_varint(uint64_t value) {
+  // Mark noinline to prevent code bloat from inlining into every caller
+  __attribute__((noinline)) void encode_varint(uint64_t value) {
     auto buffer = this->buffer_;
     size_t start = buffer->size();