fix(naming): resolve naming-convention warnings from Plugin Check

[faisalahammad]

Summary

Fix naming-convention warnings flagged by the WordPress Plugin Check report. Renames unprefixed functions, renames the meta box field interface to follow LLMS_ class prefix convention, and renames the interface file to match WordPress file naming standards. Backward compatibility preserved via deprecated wrappers.

Changes

Function Renames (includes/functions/llms.functions.course.php)

Before:

function get_course( $course_id ) { ... }
function get_lesson( $lesson_id ) { ... }

After:

function llms_get_course( $course_id ) { ... }
function llms_get_lesson( $lesson_id ) { ... }

Why: Unprefixed functions risk collisions with other plugins. Added llms_ prefix per coding standards. Old functions kept as deprecated wrappers calling the new ones.

Template Function Renames (includes/llms.template.functions.php)

Before:

function get_course_data( $course_id ) { ... }
function get_lesson_data( $lesson_id ) { ... }
function get_payment_options( $order_id ) { ... }

After:

function llms_get_course_data( $course_id ) { ... }
function llms_get_lesson_data( $lesson_id ) { ... }
function llms_get_payment_options( $order_id ) { ... }

Why: Same prefix issue. Deprecated wrappers maintain backward compatibility.

Interface Rename (Meta Box Fields)

Before:

interface Meta_Box_Field_Interface { ... }

After:

interface LLMS_Meta_Box_Field_Interface { ... }

Why: Core classes must use LLMS_ prefix per coding standards. Updated all 19 implementing classes and the class loader.

File Rename

Before: includes/admin/meta-boxes/fields/interface.meta.box.field.php

After: includes/admin/meta-boxes/fields/class-llms-metabox-field-interface.php

Why: WordPress file naming standard requires class-llms-<name>.php format.

Testing

Test 1: Backward compatibility

1. Call get_course( $id ) in a theme or plugin
2. Verify it returns same result as llms_get_course( $id )
3. Check deprecated function triggers notice in debug mode

Result: Old functions work, new functions work, deprecation notices fire correctly.

Test 2: Meta box fields

1. Open course/lesson/membership edit screen
2. Verify all meta box fields render correctly
3. Save and confirm data persists

Result: All field types (text, textarea, editor, checkbox, select, etc.) work as expected.