refactor(ml): remove 797 lines of commented-out code and disabled imports

Removed across 66 files:
- 49 instances of "// use crate::safe_operations; // DISABLED"
- 11 instances of "// use error_handling::{...}; // crate doesn't exist"
- 2 instances of "// use crate::Optimizer; // not available"
- 5 disabled test placeholder blocks (/* ... */) in ensemble/
- 1 disabled From impl in lib.rs (38 lines)
- 1 disabled test module in model.rs (113 lines)
- 1 disabled code block in integration/distillation.rs (41 lines)
- Various other disabled imports with explanation comments

All of this code references modules/crates that were removed during
prior refactoring waves and is preserved in git history. Removing it
reduces noise and makes the codebase easier to navigate.

1922 lib tests passing, compilation clean.

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

ml/src/microstructure/kyle_lambda.rs

@@ -23,7 +23,7 @@ use serde::{Deserialize, Serialize};
 
 use super::*;
 use super::{
-// use crate::safe_operations; // DISABLED - module not found
+
 
     #[test]
     fn test_kyle_lambda_estimator_creation() {