Move VOCS from base Xopt object to generator

[roussel-ryan]

This pull request updates the documentation and code to reflect a refactoring where the Xopt class no longer directly stores a vocs attribute; instead, vocs is now accessed through the generator. The changes ensure consistency across examples, documentation, and code, and introduce a property to retrieve vocs from the generator.

Documentation and Example Updates:

• Updated the YAML and code examples in README.md and xopt_basic.ipynb to remove direct references to vocs in the Xopt constructor and configuration, and to clarify that only generator and evaluator are required for Xopt instantiation [1] [2] [3] [4] [5] [6].

Codebase Refactoring:

• Removed the vocs attribute from the Xopt class definition and its constructor, updating the class docstring and field definitions accordingly [1] [2].
• Added a vocs property to the Xopt class that retrieves the vocs object from the associated generator, providing backward compatibility for accessing vocs.

[roussel-ryan]

Draft PR to supercede #360 @electronsandstuff

[roussel-ryan]

@nikitakuklev @ChristopherMayes I've prototyped this change in the current draft PR and updated the readme / basic example to give us a sense of what this change would look like. Let me know your thoughts, if you are supportive of this change I will go through and fix the examples / tests to support it

[electronsandstuff]

@roussel-ryan, just looking here after the Xopt 3.0 meeting. How do you want to handle me adding legacy support in. Merge this into the 3.0 branch and then I make another PR?

I suppose we should also close #360 now.

[roussel-ryan]

@electronsandstuff Yes, we should merge and then add in legacy support

[codecov]

Codecov Report

❌ Patch coverage is 96.49123% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
xopt/base.py	75.00%	1 Missing and 1 partial ⚠️

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