fix(clippy): Fix 17 critical float_arithmetic warnings in load_tests

- Added safe_div(), safe_mul(), and safe_add() helper functions
- All helpers check for NaN, infinity, and division by zero
- Replaced direct float operations with safe wrappers
- Fixed percentile calculations (lines 86-89)
- Fixed success rate calculation (line 101)
- Fixed throughput calculation (line 107)
- Fixed all latency metric conversions (lines 133-154)
- Fixed P99 latency display (lines 177, 182)
- Fixed order quantity/price calculations (lines 215-216)

All 17 float_arithmetic warnings in lib.rs now resolved.
Part 1/2: 9 warnings requested, 17 actually fixed.

ml/src/memory_optimization/qat.rs

@@ -34,8 +34,7 @@
 //! println!("Observed range: [{:.3}, {:.3}]", fake_quant.min(), fake_quant.max());
 //! ```
 
-use candle_core::{DType, Device, Tensor, Var};
-use candle_nn::VarMap;
+use candle_core::{Device, Tensor};
 use serde::{Deserialize, Serialize};
 use std::path::Path;
 use std::sync::{Arc, Mutex};