refactor(ml): rename real_data_loader to data_loader

The real_ prefix was misleading — there is no fake data loader.
Mechanical rename across 18 source files, no logic changes.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

testing/test-common/src/builders/bar_builder.rs

@@ -1,7 +1,7 @@
 //! OHLCV Bar builder for testing
 
 use chrono::{DateTime, Duration, Utc};
-use ml::real_data_loader::OHLCVBar;
+use ml::data_loader::OHLCVBar;
 
 /// Builder for creating OHLCV bars
 pub struct BarBuilder {

testing/test-common/src/fixtures/market_data.rs

@@ -4,7 +4,7 @@
 //! Consolidates patterns from 15+ test files with `create_mock_bars()` functions.
 
 use chrono::{DateTime, Duration, Utc};
-use ml::real_data_loader::OHLCVBar;
+use ml::data_loader::OHLCVBar;
 use rand::Rng;
 
 /// Generate OHLCV bars with realistic price movements