refactor: Remove deprecated code and clean up pre-v3.1 remnants

- Remove deprecated sync methods (get_latest_bar_sync)
- Delete debug example files (debug_fvg_indicator.py, debug_orderblock_indicator.py)
- Update documentation examples to use async-only patterns
- Clean up placeholder comments in indicators module
- Fix trailing whitespace issues
- Maintain backward compatibility for deprecated callbacks per v3.x policy

This cleanup improves code consistency with the v3.1+ async-only architecture
while preserving backward compatibility where required.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: TexasCoding

examples/debug_fvg_indicator.py

@@ -313,10 +313,6 @@ def calculate(
         )
 
 
-# Add similar classes for BearishEngulfing, MorningStar, etc.
-
-# For brevity, stopping here. You can add more similarly.
-
 # Convenience functions
 
 
@@ -334,6 +330,3 @@ def calculate_shootingstar(data: pl.DataFrame, **kwargs: Any) -> pl.DataFrame:
 
 def calculate_bullishengulfing(data: pl.DataFrame, **kwargs: Any) -> pl.DataFrame:
     return BullishEngulfing().calculate(data, **kwargs)
-
-
-# Add more convenience functions as classes are added