Fix compilation errors caused by Kyori Adventure API ClickEvent.Payload removal

[Copilot]

The project was failing to compile due to missing payloadType() and payload() methods on ClickEvent, as the newer ClickEvent.Payload API is not present in the currently targeted version of the Kyori Adventure API.

Changes

• MineDownParser.java: Replaced payload type inference and casting logic with a direct pass-through of the string value using ClickEvent.value().
• MineDownStringifier.java: Updated definitions building to pull the payload directly via clickEvent.value() rather than switching on ClickEvent.Payload subclasses.
• Replacer.java: Replaced custom/text payload handling with direct string replacement on clickEvent.value().

Example

Previously, click event payloads were handled using types:

ClickEvent.Payload payload = clickEvent.payload();
if (payload instanceof ClickEvent.Payload.Text) { ... }

Now, they are retrieved directly as strings:

String payload = clickEvent.value();