refactor: eliminate candle from entire workspace — tests, examples, Cargo.toml

Final cleanup:
- 61 test files + 5 example files: candle imports replaced
- 8 testing/integration files: migrated to cudarc/ml-core types
- 3 services/trading_service test files: migrated
- Root Cargo.toml: candle-core, candle-nn removed from [workspace.dependencies]
- crates/ml/Cargo.toml: candle-nn dependency removed
- testing/e2e/Cargo.toml: candle-core dependency removed

Zero active candle_core/candle_nn/candle_optimisers code references remain.
Zero candle dependency declarations in any Cargo.toml.
Remaining "candle" strings are exclusively in doc comments.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/ml/Cargo.toml

@@ -102,14 +102,7 @@ data = { path = "../data" }
 sqlx.workspace = true
 
 
-# Essential ML frameworks for HFT inference - CUDA OPTIONAL
-# Using specific git rev (971e7ed0) for cudarc 0.19.x CUDA 13.0 compatibility
-# Rev 971e7ed0 is v0.9.2 + cudarc 0.19.1 upgrade (resolves to 0.19.3 via semver)
-# CUDA features are optional - controlled by 'cuda' feature flag
-candle-core = { git = "https://github.com/huggingface/candle", rev = "971e7ed0" }  # Base without GPU
-candle-nn = { git = "https://github.com/huggingface/candle", rev = "971e7ed0" }
-# Use git version of candle-optimisers to match candle version
-candle-optimisers = { git = "https://github.com/KGrewal1/optimisers" }  # Base without GPU
+# candle-core, candle-nn, candle-optimisers — REMOVED (replaced by ml-core native CUDA autograd)
 
 # HEAVY ML FRAMEWORKS REMOVED - MOVED TO ml_training_service
 # ort (ONNX Runtime) - REMOVED (1000+ dependencies alone!)