feat: add Jupyter Notebook / IPython magic integration (#454)

Add %%backtest cell magic and %backtest line magic for running
backtests directly in Jupyter notebooks.

- %%backtest: define a strategy inline and run a backtest in one cell
- %backtest: run a backtest from an existing strategy file
- Supports both event-driven and vectorized backtesting (--vectorized)
- Parameters: --start, --end, --initial-amount, --market, --trading-symbol,
  -o (output variable), --show-report, --show-progress, --risk-free-rate
- Extension loaded via %load_ext investing_algorithm_framework
- Includes unit tests for parser, date parsing, strategy discovery, and
  extension registration

Closes #454

Author: MDUYN

investing_algorithm_framework/__init__.py

@@ -254,4 +254,13 @@
     "VolumeBasedFill",
     "FXRateProvider",
     "StaticFXRateProvider",
+    "load_ipython_extension",
 ]
+
+
+def load_ipython_extension(ipython):
+    """Allow ``%load_ext investing_algorithm_framework`` to register
+    the ``%backtest`` / ``%%backtest`` magic commands."""
+    from investing_algorithm_framework.notebook import load_ipython_extension \
+        as _load
+    _load(ipython)

investing_algorithm_framework/notebook/__init__.py

@@ -0,0 +1,3 @@
+from .magic import load_ipython_extension
+
+__all__ = ["load_ipython_extension"]