fix(object-cache): ensure wp_cache_delete returns boolean

[faisalahammad]

Summary

Guarantees that wp_cache_delete() and WP_Object_Cache::delete() strictly return a boolean (true or false) rather than null. This prevents PHP TypeError fatal exceptions in PHP 8.x when standard object cache functions are called.

Fixes #924

Changes

Object Cache (src/object.lib.php & src/object-cache-wp.cls.php)

Before:

function wp_cache_delete( $key, $group = '' ) {
	global $wp_object_cache;

	return $wp_object_cache->delete( $key, $group );
}

After:

function wp_cache_delete( $key, $group = '' ) {
	global $wp_object_cache;

	if ( ! is_object( $wp_object_cache ) ) {
		return false;
	}

	return (bool) $wp_object_cache->delete( $key, $group );
}

Why: Directly returning the object cache method call could return null if the instance was uninitialized or returned non-boolean values. Adding an is_object() check and explicit (bool) typecast guarantees a boolean return value.

WP Object Cache Class (src/object-cache-wp.cls.php)

Before:

if ( $this->_object_cache->is_non_persistent( $group ) ) {
	return false;
}

return $this->_object_cache->delete( $id );

After:

if ( $this->is_non_persistent( $group ) || ! is_object( $this->_object_cache ) ) {
	return $found;
}

return (bool) $this->_object_cache->delete( $id );

Why: Ensures deletion from runtime memory is returned for non-persistent groups or missing instances, and persistent store deletion output is explicitly cast to bool.

Testing

Test 1: Delete cache key

1. Run wp_cache_delete( 'test_key', 'default' ).
2. Confirm return type is boolean false (or true if item exists) and never null.

Test 2: Delete cache key with uninitialized object cache

1. Set $wp_object_cache = null and invoke wp_cache_delete( 'test_key' ).
2. Confirm return value is false without throwing PHP TypeError.

[hi-hai]

Please use dev branch as the base

[faisalahammad]

Rebased branch onto dev and updated target base to dev branch.

[faisalahammad]

Resolved conflicts. PR is now clean against dev branch.