Separate forward map

[LucaMantani]

This PR aims at separating the definition of the forward map from the pdf_model, granting us further flexibility to implement generalisations such as the addition of nuisance parameters or eft Wilson coefficients.

The main changes are:

• remove pred_and_pdf function
• Definition of an abstract class ForwardMap, which requires always the implementation of a __call__method with signature (pdf_grid_func, fk_arrays, params) -> predictions, pdf
• The implementation of a particular case, which is the one we are currently using that does only PDF fitting.
• Params are all the parameters of interest, and the first n_pdf_params are always assumed to be the pdf ones.

[codecov]

Codecov Report

❌ Patch coverage is 98.21429% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 95.20%. Comparing base (cf4d16e) to head (22207f3).
⚠️ Report is 23 commits behind head on main.

Files with missing lines	Patch %	Lines
colibri/forward_map.py	96.66%	1 Missing ⚠️

❌ Your patch check has failed because the patch coverage (98.21%) is below the target coverage (100.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #428      +/-   ##
==========================================
+ Coverage   94.96%   95.20%   +0.23%     
==========================================
  Files          31       32       +1     
  Lines        1649     1667      +18     
==========================================
+ Hits         1566     1587      +21     
+ Misses         83       80       -3     

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[LucaMantani]

Suggested change

	extra_param_names: list[str] = (),
	extra_param_names: list[str] = [],

[LucaMantani]

Suggested change

	def __init__(self, pdf_model, extra_param_names: list[str] = ()):
	def __init__(self, pdf_model, extra_param_names: list[str] = []):

[LucaMantani]

Suggested change

	def forward_map(_pred_data, pdf_model, extra_param_names=()):
	def forward_map(_pred_data, pdf_model, extra_param_names=[]):