chore: add cross_sync

[daniel-sanche]

PR 1/x for adding the sync surface for the new data client

This class adds ast transformers for converting existing async classes into sync copies.

The conversion works through the following phases:

• generate.py is called with a path, and finds all Python files in all subdirectories
• CrossSyncClassDecoratorHandler is called on each file, looking for any classes decorated with @CrossSync.export_sync
• For all classes found, they are passed through:
  • CrossSyncMethodDecoratorHandler to look for any methods annotated with CrossSync decorators (CrossSunc.convert, CrossSync.drop_method, CrossSync.pytest, etc).
  • RmAioFunctions to strip out any asyncio keywords annotated with CrossSync.rmaio()
  • SymbolReplacer to replace CrossSync with CrossSync._Sync_Impl in the codebase, and other user-specified symbol transformatioons

Next PR will add annotations to existing code to guide transformations

[mutianf]

should we default save_to_disk to true?

[daniel-sanche]

I said no, because we also use this function as part of tests later, to compare to make sure the current outputs are up to date. In that case, we'd want to see the output without writing it. But I'm fine either way

[mutianf]

I think a user of the library will want to set this to true, and we can override it for testing, let's make it default to true?

[mutianf]

what does this do? why is this only formatting async_docstring? How about sync_docstring?

[daniel-sanche]

CrossSync allows you to add variables into docstrings, and then it will replace them with a different string for sync vs async. This came up because some async methods raise exceptions when run outside of an event loop context, but that doesn't apply to sync versions. So the docstrings are mostly the same, but with an extra little note for async

On the sync side, we can replace the variables when generating the sync file. On the async side, we update the __doc__ attribute of the class as part of the class decoration process. The code itself will have template variables when you read it directly, but docs generators will read from class.__doc__ when generating content, so it will render as expected