chore(quickadapter): cleanup pre-existing docstring and logging issues

chore(quickadapter): cleanup pre-existing docstring and logging issues

- migrate_config: !r repr for config key paths in deprecation warnings
- Sphinx :param/:return: -> plain prose (top/bottom_log_return,
  price_retracement_percent, _apply_pipelines, _make_timeseries_split_datasets)
- NumPy section headers -> prose (reversal_confirmed)
- Google Args/Returns headers -> prose (get_pnl_momentum, _t_statistic,
  _effective_df, _t_critical)
- Delete boilerplate freqtrade interface override docstrings (leverage,
  plot_annotations, fit, get_trade_duration_candles, fit_regressor)
- Document make_test_set_and_weights (None, None) contract on test_size <= 0
- Simplify train() docstring (renorm detail belongs to _apply_pipelines)