Add deferred Rust backend optimizations to TODO.md

Documents post-merge optimization opportunities from PR #58 review:
- Matrix inversion efficiency (Cholesky)
- Reduce bootstrap allocations
- Consider static BLAS linking

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: igerber

TODO.md

@@ -102,9 +102,19 @@ From code review (PR #32):
 
 ---
 
+## Rust Backend Optimizations
+
+Deferred from PR #58 code review (can be done post-merge):
+
+- [ ] **Matrix inversion efficiency** (`rust/src/linalg.rs:180-194`): Use Cholesky factorization for symmetric positive-definite matrices instead of column-by-column solve
+- [ ] **Reduce bootstrap allocations** (`rust/src/bootstrap.rs`): Currently uses `Vec<Vec<f64>>` → flatten → `Array2` which allocates twice. Should allocate directly into ndarray.
+- [ ] **Consider static BLAS linking** (`rust/Cargo.toml`): Currently requires system BLAS libraries. Consider `openblas-static` or `intel-mkl-static` features for easier distribution.
+
+---
+
 ## Performance Optimizations
 
-No major performance issues identified. Potential future optimizations:
+Potential future optimizations:
 
 - [ ] JIT compilation for bootstrap loops (numba)
 - [ ] Parallel bootstrap iterations