Add observers

[Joshy3282]

Introduction

Introduces observer block

Tests

I tested this PR by doing the following (tick all that apply):

• Writing PHPUnit tests (commit these in the tests/phpunit folder)
• Playtesting using a Minecraft client (provide screenshots or a video)
• Writing a test plugin (provide the code and sample output)
• Other (provide details)
  

[RezzaAbdillah]

Why don't you add a header license?

[IvanCraft623]

the whole redstone logic is missing, which is in essence the main function of the Observer, so without a redstone implementation, there is no point in implementing it. In addition, if there is a plugin that intends to implement it properly, it will encounter the difficulty that it will not be able to overwrite the PM implementation.

Thanks for your contrubution, however redstone components cannot be implemented if there is no redstone functionality.