Add check: runtime fatal-error prevention in PHP plugin code

Summary

Add a check to detect high-risk patterns that commonly cause runtime fatals in plugins.

Why

Parse-error checks are useful, but many production fatals come from runtime assumptions (missing functions/classes/files/callbacks).

Proposed detection

Flag risky cases such as:

1. require / require_once on dynamic or unguarded paths (without file_exists/is_readable nearby).
2. Calling plugin/theme integration functions without function_exists guard.
3. Instantiating optional classes without class_exists guard.
4. Invoking dynamic callbacks without is_callable.
5. Hooking callbacks that may not exist (array/class method) without method_exists / class guard.

Acceptance criteria

1. Reports file + line.
2. Provides actionable remediation guidance in message.
3. Includes false-positive controls for clearly safe patterns.
4. Includes tests for positive and negative cases.

Inspired by

Internal Scanner checks around parse/safety, especially phpcs_parse_errors.