Classic scalar interface

The @network DSL and scalar analysis methods remain supported. The macro now requires import PowerImpedance: @network; its network semantics are unchanged. These methods operate on a mutable Network, assemble ABCD or nodal matrices, and return the historical scalar result types.

NetworkBuilder separates elements from connection declarations and supports lazy parameter grids through positional dispatch without changing scalar component implementations. Its row grammar is documented under Network construction.

The following classic entry points remain documented in the API reference: @network, Network, add!, connect!, disconnect!, composite_element, make_abcd, make_z, make_y_matrix, and the scalar overloads of the impedance and stability tools.