Add lazy superoperator types and measurement utility functions

## Summary - Add AbstractLazySuperOperator hierarchy with LazyPrePost, LazySuperSum, LazySuperTensor types for efficient lazy evaluation of superoperators - Add measurement utility functions: _drop_singular_bases, _branch_prob, _overlap, _project_and_drop for quantum measurement post-selection - Uncomment expect function for AbstractKet types that was marked TODO upstream ## New Types - `AbstractLazySuperOperator`: Base type for lazy superoperator implementations - `LazyPrePost`: Applies pre- and post-operators without storing full superoperator matrix - `LazySuperSum`: Lazy sum of multiple superoperators with factors - `LazySuperTensor`: Lazy tensor product of superoperators for composite systems ## Utility Functions - `_drop_singular_bases`: Remove dimension-1 bases after measurement - `_branch_prob`: Calculate measurement outcome probabilities - `_overlap`: Compute state/operator overlaps - `_project_and_drop`: Project onto measurement outcome and reduce dimensionality ## Test plan - [ ] Verify all new types can be constructed and used - [ ] Test lazy superoperator arithmetic operations work correctly - [ ] Confirm measurement utilities produce expected results on example systems - [ ] Check that exports work and no name conflicts exist 🤖 Generated with [Claude Code](https://claude.ai/code)