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

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TODO:

• add tests for new CrossSync functions
• add CrossSync Readme