feat(core) merge index parameters

[frostming]

Pull Request Checklist

• A news fragment is added in news/ describing what is new.
• Test cases added for changed code.

Describe what you have changed in this PR.

[codecov-commenter]

Codecov Report

Base: 85.12% // Head: 85.11% // Decreases project coverage by -0.01% ⚠️

Coverage data is based on head (de13e84) compared to base (e34a2ec).
Patch coverage: 87.50% of modified lines in pull request are covered.

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Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #1683      +/-   ##
==========================================
- Coverage   85.12%   85.11%   -0.01%     
==========================================
  Files          92       92              
  Lines        8616     8624       +8     
  Branches     1861     1867       +6     
==========================================
+ Hits         7334     7340       +6     
- Misses        862      865       +3     
+ Partials      420      419       -1     

Flag	Coverage Δ
unittests	84.92% <87.50%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/pdm/models/environment.py	66.66% <ø> (ø)
src/pdm/pytest.py	92.65% <ø> (ø)
src/pdm/cli/commands/publish/repository.py	73.17% <50.00%> (ø)
src/pdm/cli/commands/config.py	85.50% <75.00%> (+0.21%)	⬆️
src/pdm/project/config.py	83.25% <77.77%> (-0.85%)	⬇️
src/pdm/_types.py	80.00% <81.08%> (-3.88%)	⬇️
src/pdm/cli/commands/publish/__init__.py	84.70% <100.00%> (+0.18%)	⬆️
src/pdm/formats/poetry.py	85.91% <100.00%> (ø)
src/pdm/formats/requirements.py	78.62% <100.00%> (ø)
src/pdm/models/auth.py	78.37% <100.00%> (+3.37%)	⬆️
... and 3 more

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