Minor interface improvements and fix bug writing Python spec file

[taldcroft]

Description

This makes it easier to run xija_gui_fit for model spec files taken from the Ska data chandra_models repo:

• Can specify a --model-version to pick a particular version.
• Previously names like acisfp_spec_matlab were not allowed because it automatically appended _spec to the model name. Now it tries both the original model name and one with _spec appended. Doing that appending was a mistake, but it is left there for back-compatibility.

In addition this fixes a bug when writing out the Python script that will generate a spec file.

Interface impacts

Testing

Unit tests

• Mac

(ska3-flight-2025.0rc2) ➜  xija git:(improved-model-spec-file) git rev-parse --short HEAD                            
2a67036
(ska3-flight-2025.0rc2) ➜  xija git:(improved-model-spec-file) pytest xija
===================================================== test session starts ======================================================
platform darwin -- Python 3.12.8, pytest-8.3.4, pluggy-1.5.0
rootdir: /Volumes/git
configfile: pytest.ini
plugins: doctestplus-1.3.0, anyio-4.7.0, timeout-2.3.1
collected 44 items                                                                                                             

xija/tests/test_get_model_spec.py .......                                                                                [ 15%]
xija/tests/test_models.py .....................................                                                          [100%]

===================================================== 44 passed in 35.05s ======================================================

Independent check of unit tests by [REVIEWER NAME]

• [PLATFORM]:

Functional tests

Application help showing new option:

(ska3-flight-2025.0rc2) ➜  xija git:(improved-model-spec-file) python -m xija.gui_fit.app --help
WARNING: imaging routines will not be available, 
failed to import sherpa.image.ds9_backend due to 
'RuntimeErr: DS9Win unusable: Could not find ds9 on your PATH'
usage: app.py [-h] [--model-version MODEL_VERSION] [--days DAYS] [--stop STOP] [--maxiter MAXITER]
              [--fit-method FIT_METHOD] [--inherit-from INHERIT_FROM] [--set-data SET_DATA_EXPRS]
              [--quiet]
              filename

positional arguments:
  filename              Model or file name: '*.json' is a local spec file, otherwise this is a model
                        name (e.g. 'acisfp_spec_matlab') that points to a like-named JSON spec file in
                        the Ska chandra_models repo.

options:
  -h, --help            show this help message and exit
  --model-version MODEL_VERSION
                        Model version for model from chandra_models
  --days DAYS           Number of days in fit interval (default=90
  --stop STOP           Stop time of fit interval (default=model values)
  --maxiter MAXITER     Maximum number of fit iterations (default=1000)
  --fit-method FIT_METHOD
                        Sherpa fit method (simplex|moncar|levmar)
  --inherit-from INHERIT_FROM
                        Inherit par values from model spec file
  --set-data SET_DATA_EXPRS
                        Set data value as '<comp_name>=<value>'
  --quiet               Suppress screen output

Full model spec file name (acisfp_spec_matlab) with default (latest) version.

(ska3-flight-2025.0rc2) ➜  xija git:(improved-model-spec-file) python -m xija.gui_fit.app acisfp_spec_matlab
... sherpa warnings
Using model version 3.62 from chandra_models
... rest of outputs
# Brings up xija_gui_fit window as expected

Shortened model spec name (acisfp => acisfp_spec) with non-default version

(ska3-flight-2025.0rc2) ➜  xija git:(improved-model-spec-file) python -m xija.gui_fit.app acisfp --model-version=3.60 
... sherpa warnings
Using model version 3.60 from chandra_models
Fetching msid: fptemp_11 over 2025:002:23:34:30.816 to 2025:018:15:02:38.816
...
# Rest of output and normal fit window comes up

Save model to Python

First start xija_gui_fit with:

(ska3-flight-2025.0rc2) ➜  xija git:(improved-model-spec-file) python -m xija.gui_fit.app acisfp --model-version=3.60 

Then save the model as Python to acisfp_spec_3.60.py. Then run that file to remake the spec file. Previously this failed with a SyntaxError.

(ska3-flight-2025.0rc2) ➜  xija git:(improved-model-spec-file) python acisfp_spec_3.60.py acisfp_spec_3.60.json
(ska3-flight-2025.0rc2) ➜  xija git:(improved-model-spec-file) head -13 acisfp_spec_3.60.py                  
import sys
import xija

model = xija.XijaModel(
  'acisfp',
  start='2025:003:00:01:50.816',
  stop='2025:018:14:40:46.816',
  dt=328.0,
  evolve_method=2,
  rk4=0,
)