refactor: extract OHLCVDataProviderBase to eliminate duplication

Introduce an intermediate base class OHLCVDataProviderBase that handles
all shared OHLCV data provider logic:
- Constructor, copy(), get_data(), prepare_backtest_data(), get_backtest_data()
- CSV storage helpers, date range resolution, number of data points
- Fixes bug: create_start_date was missing from Yahoo/AV/Polygon providers

Concrete providers now only implement:
- market_name, timeframe_map (class attributes)
- _download_ohlcv() (API-specific download)
- _validate_symbol() (optional, Yahoo only)

Reduces Yahoo/AlphaVantage/Polygon from ~1,851 lines to ~1,033 total (44% reduction).
CCXT intentionally excluded (different pattern: exchange-based detection, pagination, ticker support).

Author: MDUYN

investing_algorithm_framework/__init__.py

@@ -28,7 +28,8 @@
 from .infrastructure import AzureBlobStorageStateHandler, \
     CSVOHLCVDataProvider, CSVTickerDataProvider, \
     CCXTOHLCVDataProvider, CCXTTickerDataProvider, \
-    PandasOHLCVDataProvider, YahooOHLCVDataProvider, \
+    PandasOHLCVDataProvider, OHLCVDataProviderBase, \
+    YahooOHLCVDataProvider, \
     AlphaVantageOHLCVDataProvider, PolygonOHLCVDataProvider, \
     AWSS3StorageStateHandler
 from .create_app import create_app
@@ -117,6 +118,7 @@
     'CSVTickerDataProvider',
     "CCXTOHLCVDataProvider",
     "CCXTTickerDataProvider",
+    "OHLCVDataProviderBase",
     "YahooOHLCVDataProvider",
     "AlphaVantageOHLCVDataProvider",
     "PolygonOHLCVDataProvider",

investing_algorithm_framework/infrastructure/__init__.py

@@ -14,6 +14,7 @@
     CSVTickerDataProvider, get_default_data_providers, \
     get_default_ohlcv_data_providers, CCXTOHLCVDataProvider, \
     CCXTTickerDataProvider, PandasOHLCVDataProvider, \
+    OHLCVDataProviderBase, \
     YahooOHLCVDataProvider, AlphaVantageOHLCVDataProvider, \
     PolygonOHLCVDataProvider
 from .order_executors import CCXTOrderExecutor, BacktestOrderExecutor
@@ -53,6 +54,7 @@
     "CCXTTickerDataProvider",
     "BacktestOrderExecutor",
     "PandasOHLCVDataProvider",
+    "OHLCVDataProviderBase",
     "YahooOHLCVDataProvider",
     "AlphaVantageOHLCVDataProvider",
     "PolygonOHLCVDataProvider",

investing_algorithm_framework/infrastructure/data_providers/__init__.py

@@ -1,6 +1,7 @@
 from .ccxt import CCXTOHLCVDataProvider, CCXTTickerDataProvider
 from .csv import CSVOHLCVDataProvider, CSVTickerDataProvider
 from .pandas import PandasOHLCVDataProvider
+from .ohlcv_base import OHLCVDataProviderBase
 from .yahoo import YahooOHLCVDataProvider
 from .alpha_vantage import AlphaVantageOHLCVDataProvider
 from .polygon import PolygonOHLCVDataProvider
@@ -44,6 +45,7 @@ def get_default_ohlcv_data_providers():
     'CCXTTickerDataProvider',
     'get_default_data_providers',
     'get_default_ohlcv_data_providers',
+    'OHLCVDataProviderBase',
     'PandasOHLCVDataProvider',
     'YahooOHLCVDataProvider',
     'AlphaVantageOHLCVDataProvider',