Add High-Level Delay-Line and Interferometer APIs

[oameye]

QuantumInputOutput.jl already has low-level tools for modeling finite pulse delays:

coupling_delay_in(u, v, T)
coupling_delay_out(u, v, T)

However, using them currently requires a lot of manual bookkeeping: defining delay-cavity modes, constructing the two-port SLH element, padding channels, managing time-dependent symbols, and assembling the network by hand.

It would be useful to expose delay lines as first-class network components, so users can write models closer to the physical diagram.

Add a high-level delay-line constructor:

delay = delay_line(
    :d,
    a_d;
    input = u,
    delay = τ,
    T = T,
)
G = G_input ▷ delay ▷ G_system ▷ G_output

For explicit input and output modes:

delay = delay_line(
    :d,
    a_d;
    input = u,
    output = v,
    T = T,
)

where output = v could be equivalent to output = delayed_mode(u, τ).

For common delayed interferometer geometries:

mz = mach_zehnder_delay(
    input = u,
    delays = (0.0, τ),
    beamsplitter = :balanced,
    T = T,
)

G_eff = mz ▷ G_atom

Possible optional arguments:

mz = mach_zehnder_delay(
    input = u,
    delays = (τ1, τ2),
    beamsplitter = :balanced,
    phase = ϕ,
    T = T,
)

The delay-line object should probably carry both the SLH component and the required time-dependent parameter mapping.
For example:

delay.G
delay.time_parameter

or:

G_delay, time_parameter = slh(delay)

This would allow composition while keeping translation ergonomic:

G_total = G_input ▷ delay.G ▷ G_system ▷ G_output

H_QO = translate_qo(
    hamiltonian(G_total),
    b;
    time_parameter = delay.time_parameter,
)

Longer term, this could become more seamless if composable network components carry their own time parameters.