mutable/matrix Design

Responsibilities

• Provide an execution-oriented Matrix[T] with row-major Array[T] storage across supported backends.
• Keep live row, column, and transpose views connected to the underlying matrix.
• Keep checked APIs for runtime failures while preserving explicit unchecked_* methods for legacy contracts.

Invariants

• Backend-specific files may tune kernels, but they must expose the same public semantics.
• Bounds checks are explicit for matrix, view, iterator, and transpose access.
• Shared algebraic operations should stay semantically aligned with immut where both packages expose them.