[core] Convert entity vectors to static allocation for reduced memory usage (#10018)

esphome/core/helpers.h

@@ -91,6 +91,42 @@ template<> constexpr int64_t byteswap(int64_t n) { return __builtin_bswap64(n);
 
 ///@}
 
+/// @name Container utilities
+///@{
+
+/// Minimal static vector - saves memory by avoiding std::vector overhead
+template<typename T, size_t N> class StaticVector {
+ public:
+  using value_type = T;
+  using iterator = typename std::array<T, N>::iterator;
+  using const_iterator = typename std::array<T, N>::const_iterator;
+
+ private:
+  std::array<T, N> data_{};
+  size_t count_{0};
+
+ public:
+  // Minimal vector-compatible interface - only what we actually use
+  void push_back(const T &value) {
+    if (count_ < N) {
+      data_[count_++] = value;
+    }
+  }
+
+  size_t size() const { return count_; }
+
+  T &operator[](size_t i) { return data_[i]; }
+  const T &operator[](size_t i) const { return data_[i]; }
+
+  // For range-based for loops
+  iterator begin() { return data_.begin(); }
+  iterator end() { return data_.begin() + count_; }
+  const_iterator begin() const { return data_.begin(); }
+  const_iterator end() const { return data_.begin() + count_; }
+};
+
+///@}
+
 /// @name Mathematics
 ///@{