feat(1314): add unclosed ob_start check

[faisalahammad]

Summary

Adds a new performance check to detect ob_start() calls that are not closed within the same scope. This prevents unpredictable behaviour caused by misaligned output buffers in shared environments.

Fixes #1314

Changes

includes/Checker/Checks/Performance/Unclosed_Ob_Start_Check.php

Before:

// File did not exist

After:

class Unclosed_Ob_Start_Check extends Abstract_File_Check {
	// ... (implements token parsing to track ob_start/close depth)
}

Why: A custom static analysis implementation utilizing token_get_all() accurately tracks block scope (T_FUNCTION, {, }) to ensure every ob_start() is reliably paired with a closing function on the same scope level.

includes/Checker/Default_Check_Repository.php

Before:

				'wp_functions_compatibility' => new Checks\Plugin_Repo\WP_Functions_Compatibility_Check(),
			)

After:

				'wp_functions_compatibility' => new Checks\Plugin_Repo\WP_Functions_Compatibility_Check(),
				'unclosed_ob_start'          => new Checks\Performance\Unclosed_Ob_Start_Check(),
			)

Why: Registers the newly created check to be automatically instantiated when scanning plugins.

Testing

Test 1: Unclosed ob_start Detection

1. Create a dummy plugin calling ob_start(); at the root without closing it, and inside a function but conditionally closed inside an if block.
2. Run wp plugin check <dummy-plugin>.
3. Verify that the command flags the unpaired ob_start() calls on the specific lines as performance warnings.

Result: Works as expected

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Co-authored-by: faisalahammad <faisalahammad@git.wordpress.org>
Co-authored-by: davidperezgar <davidperez@git.wordpress.org>

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