Improve error reporting in random extension (#9071)

* Use `php_random_bytes_throw()` in Secure engine's generate()

This exposes the underlying exception, improving debugging:

    Fatal error: Uncaught Exception: Cannot open source device in php-src/test.php:5
    Stack trace:
    #0 php-src/test.php(5): Random\Engine\Secure->generate()
    #1 {main}

    Next RuntimeException: Random number generation failed in php-src/test.php:5
    Stack trace:
    #0 php-src/test.php(5): Random\Engine\Secure->generate()
    #1 {main}
      thrown in php-src/test.php on line 5

* Use `php_random_int_throw()` in Secure engine's range()

This exposes the underlying exception, improving debugging:

    Exception: Cannot open source device in php-src/test.php:17
    Stack trace:
    #0 php-src/test.php(17): Random\Randomizer->getInt(1, 3)
    #1 {main}

    Next RuntimeException: Random number generation failed in php-src/test.php:17
    Stack trace:
    #0 php-src/test.php(17): Random\Randomizer->getInt(1, 3)
    #1 {main}

* Throw exception when a user engine returns an empty string

This improves debugging, because the actual reason for the failure is available
as a previous Exception:

    DomainException: The returned string must not be empty in php-src/test.php:17
    Stack trace:
    #0 php-src/test.php(17): Random\Randomizer->getBytes(123)
    #1 {main}

    Next RuntimeException: Random number generation failed in php-src/test.php:17
    Stack trace:
    #0 php-src/test.php(17): Random\Randomizer->getBytes(123)
    #1 {main}

* Throw exception when the range selector fails to get acceptable numbers in 50 attempts

This improves debugging, because the actual reason for the failure is available
as a previous Exception:

    RuntimeException: Failed to generate an acceptable random number in 50 attempts in php-src/test.php:17
    Stack trace:
    #0 php-src/test.php(17): Random\Randomizer->getInt(1, 3)
    #1 {main}

    Next RuntimeException: Random number generation failed in php-src/test.php:17
    Stack trace:
    #0 php-src/test.php(17): Random\Randomizer->getInt(1, 3)
    #1 {main}

* Improve user_unsafe test

Select parameters for ->getInt() that will actually lead to unsafe behavior.

* Fix user_unsafe test

If an engine fails once it will be permanently poisoned by setting
`->last_unsafe`. This is undesirable for the test, because it skews the
results.

Fix this by creating a fresh engine for each "assertion".

* Remove duplication in user_unsafe.phpt

* Catch `Throwable` in user_unsafe.phpt

As we print the full stringified exception we implicitly assert the type of the
exception. No need to be overly specific in the catch block.

* Throw an error if an engine returns an empty string

* Throw an Error if range fails to find an acceptable number in 50 attempts

ext/random/engine_user.c

@@ -50,6 +50,7 @@ static uint64_t generate(php_random_status *status)
 			result += ((uint64_t) (unsigned char) Z_STRVAL(retval)[i]) << (8 * i);
 		}
 	} else {
+		zend_throw_error(NULL, "A random engine must return a non-empty string");
 		status->last_unsafe = true;
 		return 0;
 	}