[dlms_meter] Batch UART reads to reduce per-loop overhead

Replace byte-at-a-time read_byte() calls with batched read_array()
in loop(). Each read_byte() internally chains through
read_array(data, 1) -> check_read_timeout_(1) -> available(),
resulting in ~3 UART driver calls per byte. Batching into a 64-byte
stack buffer reduces this to ~3 calls per loop iteration regardless
of how many bytes are available.

Also uses vector insert() for bulk append instead of per-byte
push_back(), and caps reads to remaining buffer capacity upfront
to avoid over-reading from UART.

esphome/components/debug/debug_esp8266.cpp

@@ -1,7 +1,6 @@
 #include "debug_component.h"
 #ifdef USE_ESP8266
 #include "esphome/core/log.h"
-#include "esphome/core/progmem.h"
 #include <Esp.h>
 
 extern "C" {
@@ -20,38 +19,27 @@ namespace debug {
 
 static const char *const TAG = "debug";
 
-// PROGMEM string table for reset reasons, indexed by reason code (0-6), with "Unknown" as fallback
-// clang-format off
-PROGMEM_STRING_TABLE(ResetReasonStrings,
-  "Power On",                  // 0 = REASON_DEFAULT_RST
-  "Hardware Watchdog",         // 1 = REASON_WDT_RST
-  "Exception",                 // 2 = REASON_EXCEPTION_RST
-  "Software Watchdog",         // 3 = REASON_SOFT_WDT_RST
-  "Software/System restart",   // 4 = REASON_SOFT_RESTART
-  "Deep-Sleep Wake",           // 5 = REASON_DEEP_SLEEP_AWAKE
-  "External System",           // 6 = REASON_EXT_SYS_RST
-  "Unknown"                    // 7 = fallback
-);
-// clang-format on
-static_assert(REASON_DEFAULT_RST == 0, "Reset reason enum values must match table indices");
-static_assert(REASON_WDT_RST == 1, "Reset reason enum values must match table indices");
-static_assert(REASON_EXCEPTION_RST == 2, "Reset reason enum values must match table indices");
-static_assert(REASON_SOFT_WDT_RST == 3, "Reset reason enum values must match table indices");
-static_assert(REASON_SOFT_RESTART == 4, "Reset reason enum values must match table indices");
-static_assert(REASON_DEEP_SLEEP_AWAKE == 5, "Reset reason enum values must match table indices");
-static_assert(REASON_EXT_SYS_RST == 6, "Reset reason enum values must match table indices");
-
-// PROGMEM string table for flash chip modes, indexed by mode code (0-3), with "UNKNOWN" as fallback
-PROGMEM_STRING_TABLE(FlashModeStrings, "QIO", "QOUT", "DIO", "DOUT", "UNKNOWN");
-static_assert(FM_QIO == 0, "Flash mode enum values must match table indices");
-static_assert(FM_QOUT == 1, "Flash mode enum values must match table indices");
-static_assert(FM_DIO == 2, "Flash mode enum values must match table indices");
-static_assert(FM_DOUT == 3, "Flash mode enum values must match table indices");
-
 // Get reset reason string from reason code (no heap allocation)
 // Returns LogString* pointing to flash (PROGMEM) on ESP8266
 static const LogString *get_reset_reason_str(uint32_t reason) {
-  return ResetReasonStrings::get_log_str(static_cast<uint8_t>(reason), ResetReasonStrings::LAST_INDEX);
+  switch (reason) {
+    case REASON_DEFAULT_RST:
+      return LOG_STR("Power On");
+    case REASON_WDT_RST:
+      return LOG_STR("Hardware Watchdog");
+    case REASON_EXCEPTION_RST:
+      return LOG_STR("Exception");
+    case REASON_SOFT_WDT_RST:
+      return LOG_STR("Software Watchdog");
+    case REASON_SOFT_RESTART:
+      return LOG_STR("Software/System restart");
+    case REASON_DEEP_SLEEP_AWAKE:
+      return LOG_STR("Deep-Sleep Wake");
+    case REASON_EXT_SYS_RST:
+      return LOG_STR("External System");
+    default:
+      return LOG_STR("Unknown");
+  }
 }
 
 // Size for core version hex buffer
@@ -104,9 +92,23 @@ size_t DebugComponent::get_device_info_(std::span<char, DEVICE_INFO_BUFFER_SIZE>
   constexpr size_t size = DEVICE_INFO_BUFFER_SIZE;
   char *buf = buffer.data();
 
-  const LogString *flash_mode = FlashModeStrings::get_log_str(
-      static_cast<uint8_t>(ESP.getFlashChipMode()),  // NOLINT(readability-static-accessed-through-instance)
-      FlashModeStrings::LAST_INDEX);
+  const LogString *flash_mode;
+  switch (ESP.getFlashChipMode()) {  // NOLINT(readability-static-accessed-through-instance)
+    case FM_QIO:
+      flash_mode = LOG_STR("QIO");
+      break;
+    case FM_QOUT:
+      flash_mode = LOG_STR("QOUT");
+      break;
+    case FM_DIO:
+      flash_mode = LOG_STR("DIO");
+      break;
+    case FM_DOUT:
+      flash_mode = LOG_STR("DOUT");
+      break;
+    default:
+      flash_mode = LOG_STR("UNKNOWN");
+  }
   uint32_t flash_size = ESP.getFlashChipSize() / 1024;       // NOLINT(readability-static-accessed-through-instance)
   uint32_t flash_speed = ESP.getFlashChipSpeed() / 1000000;  // NOLINT(readability-static-accessed-through-instance)
   ESP_LOGD(TAG, "Flash Chip: Size=%" PRIu32 "kB Speed=%" PRIu32 "MHz Mode=%s", flash_size, flash_speed,

esphome/components/dlms_meter/dlms_meter.cpp

@@ -28,15 +28,28 @@ void DlmsMeterComponent::dump_config() {
 
 void DlmsMeterComponent::loop() {
   // Read while data is available, netznoe uses two frames so allow 2x max frame length
-  while (this->available()) {
-    if (this->receive_buffer_.size() >= MBUS_MAX_FRAME_LENGTH * 2) {
+  int avail = this->available();
+  if (avail > 0) {
+    size_t remaining = MBUS_MAX_FRAME_LENGTH * 2 - this->receive_buffer_.size();
+    if (remaining == 0) {
       ESP_LOGW(TAG, "Receive buffer full, dropping remaining bytes");
-      break;
+    } else {
+      // Read all available bytes in batches to reduce UART call overhead.
+      // Cap reads to remaining buffer capacity.
+      if (static_cast<size_t>(avail) > remaining) {
+        avail = remaining;
+      }
+      uint8_t buf[64];
+      while (avail > 0) {
+        size_t to_read = std::min(static_cast<size_t>(avail), sizeof(buf));
+        if (!this->read_array(buf, to_read)) {
+          break;
+        }
+        avail -= to_read;
+        this->receive_buffer_.insert(this->receive_buffer_.end(), buf, buf + to_read);
+        this->last_read_ = millis();
+      }
     }
-    uint8_t c;
-    this->read_byte(&c);
-    this->receive_buffer_.push_back(c);
-    this->last_read_ = millis();
   }
 
   if (!this->receive_buffer_.empty() && millis() - this->last_read_ > this->read_timeout_) {