refactor of group 6 (utilities and helpers) completed: improve utilities,...

refactor of group 6 (utilities and helpers) completed: improve utilities, precision handling, and test stability

- Implement secure `ast`-based expression evaluation in `_safe_eval_math` to replace `eval()`
- Refactor `run_batched` and its wrapper to use `SamplingContext` object, reducing positional arguments
- Update `_cast_warmup_state_dtype` to a fail-fast approach with CRITICAL logging and RuntimeError
- Add comprehensive module and function docstrings to `logging_utils.py` and `utils.py`
- Remove dead code, unused imports, and redundant local imports across utility modules
- Simplify boolean comparisons in `_configure_jax_precision` for better idiomatic clarity
- Add `tests/test_group6_utils.py` with 23 unit tests covering utility and helper functions
- Resolve test suite isolation issues by implementing global JAX state reset in `conftest.py`