This PR adds support for configuring JSON encoding options at the client level. This allows setting default JSON encoding behavior for all requests made by a client instance.

Feature

• Added json_encode_options to client configuration
• Options are applied when encoding JSON request bodies
• Supports all standard PHP JSON encoding options (e.g., JSON_UNESCAPED_UNICODE, JSON_INVALID_UTF8_SUBSTITUTE)

Added Tests

• Test client-level JSON encoding configuration
• Test nested Unicode characters and invalid UTF-8 handling
• Test JSON encoding options inheritance
• Test supplementary plane characters (4-byte Unicode)
• Test middleware chain cleanup

Example Usage

// Configure client to preserve Unicode characters
$client = new Client([
    'json_encode_options' => JSON_UNESCAPED_UNICODE | JSON_INVALID_UTF8_SUBSTITUTE
]);

// All JSON requests will use these encoding options
$response = $client->post('/', [
    'json' => ['greeting' => '👋 Hello']
]); // Will preserve Unicode characters in outpu