v0.2.0

Adds the photonic molecule: a two-ring coupled-mode model (photonic_molecule), output spectra with per-mode port couplings (output_variance_ports), and the exact instability threshold (molecule_threshold).

Every stated property is asserted in the test suite rather than claimed: exact reduction to the single ring at zero coupling; exact vacuum from a passive molecule at every port, coupling and frequency; supermode splitting of exactly 2J; the resonant threshold mu = 1 + J^2/gamma (Hopf branch 1 + gamma beyond J = gamma); the quarter-turn quadrature rotation of the -iJ hop; the exact zero-frequency equivalence of the auxiliary-ring port to an effective single mode; and a J^2/gamma = 3 molecule reaching 6 dB detected squeezing through the auxiliary port while the Kerr ring has no extraction port. 15 tests total.

Also corrects cff-version in CITATION.cff to 1.2.0 (the format version; the file previously carried the package version there).

Install: pip install sqzcomb