The pytest marker slycot is equivalent to the slycotonly decorator,
and also allows slycot tests to be included or excluded at the pytest
command-line.

The pytest marker cvxopt is equivalent to the cvxoptonly decorator,
and also allows cvxopt tests to be included or excluded at the pytest
command-line.

Use pytest markers for slycot, cvxopt, and pandas tests

Test solvers dependent on Slycot when "slycot" test marker is
specified.  These tests are now parametrized by method.

Use custom pytest mark `noslycot` for tests where slycot must not be
installed to pass.

Extend use of pyest mark `slycot` to other tests using Slycot
functions.

pytest marks for slycot, part 2

fix return shape for place_acker (#1190)

Fix bandwidth function for DT systems

Preserve explicitly shaped empty state-space matrices so linearized interconnections with zero inputs and nonzero outputs keep a (noutputs, 0) D matrix.

Co-authored-by: OpenAI Codex <[email protected]>

Preserve automatic near-axis indentation when no direction is passed, but let explicit left/right override pole-side selection for poles within the indent radius.

Fixes #1194

…matrix

Fix zero-input interconnect D matrix shape

Honor explicit Nyquist indent direction near imaginary axis

Squash-merge of #1216

Fixes #1204