Code clean up with declare strict and php stan level 9 checks

add "declare(strict_types=1);" to all pages

Add a json handler class to handle that json_decode always returns array<mixed> and throws error otherwise
On failure these will throw the normal JSON encoded error was FAILURE with code "J-" and the number is the json error
If 0 then the return was null or some other problem that did not return an array

amount is float and not string and checks are done that the returned value is a float

various updates for phpdoc array delcarations
- curl header is array<int, string>
- the log array is proper declared as array with string key and a list of mixed arrays

src/Response/CancelResponse.php

@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace gullevek\AmazonIncentives\Response;
 
 use gullevek\AmazonIncentives\Debug\AmazonDebug;