New version: Piccolo v1.18.0

[JuliaRegistrator]

• Registering package: Piccolo
• Repository: https://github.com/harmoniqs/Piccolo.jl
• Created by: @jack-champagne
• Version: v1.18.0
• Commit: f11c764d35e2d3641f1b93911b5fc2663439823a
• Reviewed by: @jack-champagne
• Reference: harmoniqs/Piccolo.jl@f11c764#commitcomment-187774277
• Description: A Julia package for solving quantum optimal control problems using direct trajectory optimization.
• Release notes:

## Changes

- Fix `PiccoloMakieExt` precompilation failure by requiring DirectTrajOpt 0.9.5, which provides `AbstractIntermediateCallback` (the supertype used by the live pulse-plot callback). The previous `0.8, 0.9` bound could resolve to a version lacking that binding.
- `CubicSplinePulse` now defaults both `R_u` and `R_du` to `0.0` (previously `1e-2`). The old penalty biased the optimiser toward flat, small-amplitude pulses and stalled fidelity (e.g. ≈0.91 vs ≈0.98+ on a 2-qubit iSWAP). `LinearSplinePulse` keeps the `1e-2` default.

## Added

- `extra_objectives` keyword on `SplinePulseProblem` for composing user-supplied objective terms (e.g. `Piccolissimo.HermiteBendingEnergyRegularizer`) into the total objective.

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