[12.x ]Introduce a JsonSchema validation rule

[lucasmichot]

Description

This PR adds a json_schema validation rule to Laravel’s validator, allowing attributes to be validated against JSON Schemas. It introduces a new JsonSchema rule class, integrates with opis/json-schema, and includes a fluent Rule::jsonSchema() helper.

This is made possible by he introduction of illuminate/json-schema, see #56903 by @nunomaduro

This is still very much Work in progress.

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What's Changed

• Added validateJsonSchema() method in ValidatesAttributes.
• Added Rule::jsonSchema(Type $schema) convenience method.
• New Illuminate\Validation\Rules\JsonSchema class with support for normalization, malformed JSON detection, and detailed error messages.
• Added opis/json-schema dependency.
• Test coverage for valid/invalid payloads, malformed JSON, nested schemas, arrays, enums, and required fields.

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Motivation

• Native JSON Schema validation in Laravel.
• Accurate, schema-based validation with clear error messages.

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Example

use Illuminate\Validation\Rule;
use Illuminate\JsonSchema\Types\Type;

$schema = Type::object([
    'name' => Type::string()->required(),
    'age'  => Type::integer()->min(0),
]);

$request->validate([
    'data' => [Rule::jsonSchema($schema)],
]);

[github-actions]

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[AhmedAlaa4611]

Hello @lucasmichot

Would it make sense to pass a plain array instead, and let Rule::jsonSchema() internally wrap it in Type::object()? For example:

use Illuminate\Validation\Rule;
use Illuminate\JsonSchema\Types\Type;

$schema = [
    'name' => Type::string()->required(),
    'age'  => Type::integer()->min(0),
];

$request->validate([
    'data' => [Rule::jsonSchema($schema)],
]);

I think we could simply do this by modifying the jsonSchema() method inside src/Illuminate/Validation/Rule.php to be like this:

/**
 * Create a JSON Schema validation rule.
 *
 * @param  array<string, \Illuminate\JsonSchema\Types\Type>  $schema
 * @return \Illuminate\Validation\Rules\JsonSchema
 */
public static function jsonSchema(array $schema)
{
    return new JsonSchemaRule(Type::object($schema));
}