This module provides two core types for representing quantum operators in the Pauli basis:

• : A tensor product of single-qubit Pauli operators with a global phase coefficient: c · P₀ ⊗ P₁ ⊗ ... ⊗ Pₙ₋₁
• : A sum of Pauli registers with complex coefficients, representing a general qubit Hamiltonian: H = Σₐ cₐ σₐ

Multiplication of two Pauli registers is exact and O(n): each qubit position is multiplied independently using the Pauli multiplication table, with phases accumulated into the global coefficient.