Non-linear model defaults

[dominikbach]

Fixes # .

Changed non linear model default in line with de Vries et al 2026) preprint.

Changes proposed in this pull request:

• change default filter to unidirectional
• change default flexible response dispersion to constrained, as simplest option for downstream analysis
• integrate constrained and the hidden upper_constrained option

Please test with tutorial data.

[gjheij]

Looks good to me

[dominikbach]

aSCR offset was interchangeably taken from two different sources (pspm_init and pspm_options) which had different default values. Now removed from pspm_init and only set in DCM options. Help text adjusted as well.

[dominikbach]

Current status:

f_SCR requires sigma_offset, which is currently passed via settings in line 54, and this setting field was removed. We need to create a different way of passing it. The easiest solution might be a field settings.temp  which is set in pspm_inv  (and removed at the end of the script) and read in f_SCR.