Implement level.dat reading and load the seed for use in world generation

[neeleshpoli]

Description

Adds support for reading the level.dat file in the anvil world format. With this support, the seed in the level.dat file is now used for chunk generation.

Testing

Create a world in vanilla minecraft, and load the world into pumpkin. The newly generated chunks should seamlessly blend with the already generated chunks. A sample level.dat was added to unit tests for further testing.

Checklist

Things need to be done before this Pull Request can be merged.

• Implement level.dat loading
• Code is well-formatted and adheres to project style guidelines: cargo fmt
• Code does not produce any clippy warnings: cargo clippy
• All unit tests pass: cargo test
• I added new unit tests, so other people don't accidentally break my code by changing other parts of the codebase. How?

[Snowiiii]

This should be placed not in the chunk dir.

[neeleshpoli]

I placed it in the chunk dir because this is a specific thing to the anvil world format; hence why it's in the anvil file. Do you want me to separate the level.dat loading and chunk loading?

[Snowiiii]

I would like to separate chunk loading and "general world data loading". It would also make no sense to put it into the chunk folder since it has nothing to do with chunks. Also later someone can may use a different world format while having anvil chunks or the other way around

[Snowiiii]

Looks good now. It so impressive how well everything plays together now. Our generation exactly matches the vanilla. Still have to say great job @kralverde

Thanks @neeleshpoli 👍