Write a Rust implementation of the N-Queens problem using a recursive backtracking approach. After the initial implementation, refactor the code to improve performance by: 1) Using bitwise operations for board representation. 2) Implementing iterative deepening or symmetry breaking if applicable. 3) Adding parallelism where safe. Provide the final code along with a Big-O analysis comparing the time and space complexity of the naive recursive solution versus your optimized version.