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>

lib/KOReaderSync/KOReaderCredentialStore.cpp

@@ -1,7 +1,7 @@
 #include "KOReaderCredentialStore.h"
 
 #include <HalStorage.h>
-#include <HardwareSerial.h>
+#include <Logging.h>
 #include <MD5Builder.h>
 #include <Serialization.h>
 
@@ -44,7 +44,7 @@ bool KOReaderCredentialStore::saveToFile() const {
 
   // Write username (plaintext - not particularly sensitive)
   serialization::writeString(file, username);
-  Serial.printf("[%lu] [KRS] Saving username: %s\n", millis(), username.c_str());
+  LOG_DBG("KRS", "Saving username: %s", username.c_str());
 
   // Write password (obfuscated)
   std::string obfuscatedPwd = password;
@@ -58,14 +58,14 @@ bool KOReaderCredentialStore::saveToFile() const {
   serialization::writePod(file, static_cast<uint8_t>(matchMethod));
 
   file.close();
-  Serial.printf("[%lu] [KRS] Saved KOReader credentials to file\n", millis());
+  LOG_DBG("KRS", "Saved KOReader credentials to file");
   return true;
 }
 
 bool KOReaderCredentialStore::loadFromFile() {
   FsFile file;
   if (!Storage.openFileForRead("KRS", KOREADER_FILE, file)) {
-    Serial.printf("[%lu] [KRS] No credentials file found\n", millis());
+    LOG_DBG("KRS", "No credentials file found");
     return false;
   }
 
@@ -73,7 +73,7 @@ bool KOReaderCredentialStore::loadFromFile() {
   uint8_t version;
   serialization::readPod(file, version);
   if (version != KOREADER_FILE_VERSION) {
-    Serial.printf("[%lu] [KRS] Unknown file version: %u\n", millis(), version);
+    LOG_DBG("KRS", "Unknown file version: %u", version);
     file.close();
     return false;
   }
@@ -110,14 +110,14 @@ bool KOReaderCredentialStore::loadFromFile() {
   }
 
   file.close();
-  Serial.printf("[%lu] [KRS] Loaded KOReader credentials for user: %s\n", millis(), username.c_str());
+  LOG_DBG("KRS", "Loaded KOReader credentials for user: %s", username.c_str());
   return true;
 }
 
 void KOReaderCredentialStore::setCredentials(const std::string& user, const std::string& pass) {
   username = user;
   password = pass;
-  Serial.printf("[%lu] [KRS] Set credentials for user: %s\n", millis(), user.c_str());
+  LOG_DBG("KRS", "Set credentials for user: %s", user.c_str());
 }
 
 std::string KOReaderCredentialStore::getMd5Password() const {
@@ -140,12 +140,12 @@ void KOReaderCredentialStore::clearCredentials() {
   username.clear();
   password.clear();
   saveToFile();
-  Serial.printf("[%lu] [KRS] Cleared KOReader credentials\n", millis());
+  LOG_DBG("KRS", "Cleared KOReader credentials");
 }
 
 void KOReaderCredentialStore::setServerUrl(const std::string& url) {
   serverUrl = url;
-  Serial.printf("[%lu] [KRS] Set server URL: %s\n", millis(), url.empty() ? "(default)" : url.c_str());
+  LOG_DBG("KRS", "Set server URL: %s", url.empty() ? "(default)" : url.c_str());
 }
 
 std::string KOReaderCredentialStore::getBaseUrl() const {
@@ -163,6 +163,5 @@ std::string KOReaderCredentialStore::getBaseUrl() const {
 
 void KOReaderCredentialStore::setMatchMethod(DocumentMatchMethod method) {
   matchMethod = method;
-  Serial.printf("[%lu] [KRS] Set match method: %s\n", millis(),
-                method == DocumentMatchMethod::FILENAME ? "Filename" : "Binary");
+  LOG_DBG("KRS", "Set match method: %s", method == DocumentMatchMethod::FILENAME ? "Filename" : "Binary");
 }