DescriptorBase now is a ModelBase class

[rozyczko]

DescriptorBase now inherits from NewBase instead of SerializerComponent, and uses SerializerBase for serialization. The to_dict method is introduced as the standard serialization method, with as_dict provided as an alias for backward compatibility.

The serialization interface for descriptor and parameter classes (DescriptorNumber, DescriptorArray, DescriptorAnyType, Parameter) is unified to use to_dict, replacing previous as_dict implementations.

EasyList used in MultiFitter now only accepts ModelBase members, preventing bare parameters or foreign objects from being silently ignored during fitting.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.80%. Comparing base (fd8879b) to head (c02814f).

Additional details and impacted files

@@                     Coverage Diff                     @@
##           easylist-on-multifitter     #306      +/-   ##
===========================================================
- Coverage                    83.82%   83.80%   -0.03%     
===========================================================
  Files                           68       68              
  Lines                         5348     5334      -14     
===========================================================
- Hits                          4483     4470      -13     
+ Misses                         865      864       -1     

Flag	Coverage Δ
unittests	83.80% <100.00%> (-0.03%)	⬇️

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Files with missing lines	Coverage Δ
src/easyscience/base_classes/easy_list.py	96.20% <ø> (ø)
src/easyscience/base_classes/new_base.py	100.00% <ø> (ø)
src/easyscience/fitting/multi_fitter.py	98.61% <100.00%> (+0.01%)	⬆️
src/easyscience/variable/descriptor_any_type.py	96.87% <100.00%> (ø)
src/easyscience/variable/descriptor_array.py	89.56% <100.00%> (ø)
src/easyscience/variable/descriptor_base.py	94.80% <100.00%> (+0.23%)	⬆️
src/easyscience/variable/descriptor_number.py	95.40% <100.00%> (ø)
src/easyscience/variable/parameter.py	95.31% <100.00%> (ø)