Added icdf for HalfStudentT; tests

[dalai444]

Description

Wrote ICDF for HalfStudentT as well as relevant tests.

Related Issue

• Closes #
• [ x] Related to Add icdf functions for distributions #6612

Checklist

• Checked that the pre-commit linting/style checks pass
• Included tests that prove the fix is effective or that the new feature works
• Added necessary documentation (docstrings and/or example notebooks)
• If you are a pro: each commit corresponds to a relevant logical change

Type of change

• New feature / enhancement
• Bug fix
• Documentation
• Maintenance
• Other (please specify):

---

📚 Documentation preview 📚: https://pymc--7919.org.readthedocs.build/en/7919/

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.47%. Comparing base (340e403) to head (fcdb7f1).
⚠️ Report is 32 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7919      +/-   ##
==========================================
- Coverage   91.62%   91.47%   -0.16%     
==========================================
  Files         116      116              
  Lines       18852    18939      +87     
==========================================
+ Hits        17274    17325      +51     
- Misses       1578     1614      +36     

Files with missing lines	Coverage Δ
pymc/distributions/continuous.py	98.23% <100.00%> (-0.02%)	⬇️

... and 26 files with indirect coverage changes

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[welcome]

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Congrats on merging your first pull request! 🎉 We here at PyMC are proud of you! 💖 Thank you so much for your contribution 🎁

[ricardoV94]

Thanks @dalai444