Refactor YAML Configuration Validation and Diagnostics

[KangYiYao19]

1. The addressed issue

The issue is in the Home Assistant’s YAML configuration system:

• Invalid list items inside packages (eg. strings in a list of dicts) were silently merged.
• Validation errors were unclear, where missing context about the value, location or reason are missing.
• Deprecated configuration options were not highlighted, causing users to receive no guidance on migration.

2. What I have reengineered

• Enhanced merge_packages_config() with strict type-checking for list-based domain configurations to prevent invalid items from being merged.
• Refactored stringify_invalid() and humanize_error() to produce structured diagnostics, including error categories, config paths, offending values, hints and optional documentation links.
• Added _log_deprecated_config() and updated async_hass_config_yaml() to detect deprecated configuration options and warn users during YAML loading.

3. Reengineering Strategy / Approach Used

Partial approach is used.

Only targeted components of the configuration subsystem were reengineered, rather than modifying the entire YAML loading pipeline.

• merge_packages_config() was updated to introduce strict validation for list-based configurations, while other merge logic are untouched.
• stringify_invalid() and humanize_error() were enhanced to improve error formatting without altering how other validation routines operate.
• async_hass_config_yaml() was extended with deprecated configuration detection, but its core YAML loading behavior remained unchanged.

4. Impact of Changes

• Malformed inputs can no longer silently corrupt merged configurations.
• Troubleshooting is improved as users now receive actionable feedback when validation issues occur.
• Migration support is clearer as deprecated configuration options now trigger explicit warnings with guidance for replacement.