feat: Introduce CodecheckLogger wrapper class for levelled logging

[subhanLabs]

Closes #85

What this PR does

Introduces a simple CodecheckLogger wrapper class that replaces all error_log() calls across the plugin with consistent, levelled logging.

Changes

• Added classes/Log/CodecheckLogger.php with three log levels: debug, info, error
• Replaced all error_log() calls in:
  • CodecheckPlugin.php
  • api/v1/CodecheckApiHandler.php
  • classes/CodecheckRegister/CodecheckVenueTypes.php
  • classes/CodecheckRegister/CodecheckVenueNames.php
  • classes/CodecheckRegister/CertificateIdentifierList.php

Log format

All messages are prefixed with [codecheck] and the level, e.g.:

[codecheck][debug] register() called, path=plugins/generic/codecheck
[codecheck][info] Upload file for submission: 5
[codecheck][error] YAML Parse Exception: ...