feat: Add central logging pragma (#843)

## Summary

* Definition and use of a central LOG function, that can later be
extended or completely be removed (for public use where debugging
information may not be required) to save flash by suppressing the
-DENABLE_SERIAL_LOG like in the slim branch

* **What changes are included?**

## Additional Context
* By using the central logger the usual:
```
#include <HardwareSerial.h>
...
  Serial.printf("[%lu] [WCS] Obfuscating/deobfuscating %zu bytes\n", millis(), data.size());
```
would then become
```
#include <Logging.h>
...
  LOG_DBG("WCS", "Obfuscating/deobfuscating %zu bytes", data.size());
```
You do have ``LOG_DBG`` for debug messages, ``LOG_ERR`` for error
messages and ``LOG_INF`` for informational messages. Depending on the
verbosity level defined (see below) soe of these message types will be
suppressed/not-compiled.

* The normal compilation (default) will create a firmware.elf file of
42.194.356 bytes, the same code via slim will create 42.024.048 bytes -
170.308 bytes less
* Firmware.bin : 6.469.984 bytes for default, 6.418.672 bytes for slim -
51.312 bytes less


### AI Usage

While CrossPoint doesn't have restrictions on AI tools in contributing,
please be transparent about their usage as it
helps set the right context for reviewers.

Did you use AI tools to help write this code? _NO_

---------

Co-authored-by: Xuan Son Nguyen <son@huggingface.co>

src/activities/settings/ClearCacheActivity.cpp

@@ -2,7 +2,7 @@
 
 #include <GfxRenderer.h>
 #include <HalStorage.h>
-#include <HardwareSerial.h>
+#include <Logging.h>
 
 #include "MappedInputManager.h"
 #include "components/UITheme.h"
@@ -104,12 +104,12 @@ void ClearCacheActivity::render() {
 }
 
 void ClearCacheActivity::clearCache() {
-  Serial.printf("[%lu] [CLEAR_CACHE] Clearing cache...\n", millis());
+  LOG_DBG("CLEAR_CACHE", "Clearing cache...");
 
   // Open .crosspoint directory
   auto root = Storage.open("/.crosspoint");
   if (!root || !root.isDirectory()) {
-    Serial.printf("[%lu] [CLEAR_CACHE] Failed to open cache directory\n", millis());
+    LOG_DBG("CLEAR_CACHE", "Failed to open cache directory");
     if (root) root.close();
     state = FAILED;
     updateRequired = true;
@@ -128,14 +128,14 @@ void ClearCacheActivity::clearCache() {
     // Only delete directories starting with epub_ or xtc_
     if (file.isDirectory() && (itemName.startsWith("epub_") || itemName.startsWith("xtc_"))) {
       String fullPath = "/.crosspoint/" + itemName;
-      Serial.printf("[%lu] [CLEAR_CACHE] Removing cache: %s\n", millis(), fullPath.c_str());
+      LOG_DBG("CLEAR_CACHE", "Removing cache: %s", fullPath.c_str());
 
       file.close();  // Close before attempting to delete
 
       if (Storage.removeDir(fullPath.c_str())) {
         clearedCount++;
       } else {
-        Serial.printf("[%lu] [CLEAR_CACHE] Failed to remove: %s\n", millis(), fullPath.c_str());
+        LOG_ERR("CLEAR_CACHE", "Failed to remove: %s", fullPath.c_str());
         failedCount++;
       }
     } else {
@@ -144,7 +144,7 @@ void ClearCacheActivity::clearCache() {
   }
   root.close();
 
-  Serial.printf("[%lu] [CLEAR_CACHE] Cache cleared: %d removed, %d failed\n", millis(), clearedCount, failedCount);
+  LOG_DBG("CLEAR_CACHE", "Cache cleared: %d removed, %d failed", clearedCount, failedCount);
 
   state = SUCCESS;
   updateRequired = true;
@@ -153,7 +153,7 @@ void ClearCacheActivity::clearCache() {
 void ClearCacheActivity::loop() {
   if (state == WARNING) {
     if (mappedInput.wasPressed(MappedInputManager::Button::Confirm)) {
-      Serial.printf("[%lu] [CLEAR_CACHE] User confirmed, starting cache clear\n", millis());
+      LOG_DBG("CLEAR_CACHE", "User confirmed, starting cache clear");
       xSemaphoreTake(renderingMutex, portMAX_DELAY);
       state = CLEARING;
       xSemaphoreGive(renderingMutex);
@@ -164,7 +164,7 @@ void ClearCacheActivity::loop() {
     }
 
     if (mappedInput.wasPressed(MappedInputManager::Button::Back)) {
-      Serial.printf("[%lu] [CLEAR_CACHE] User cancelled\n", millis());
+      LOG_DBG("CLEAR_CACHE", "User cancelled");
       goBack();
     }
     return;