[Depends on #3575] ParmEst: Add profile likelihood analysis for model identifiability

[sscini]

Fixes # .

Summary/Motivation:

This PR implements profile likelihood as a method for practical identifiability analysis of parmest models. This includes a new function within the experiment class in parmest.py, and a new visualization function in graphics.py

Changes proposed in this PR:

• Add profile likelihood analysis for structural identifiability based on multistart
• Add visualization tool for analyzing results
• Adjust private functions to accommodate extension
• New tests to confirm extension works as intended

TODO before converting from draft:

• Merge _Q_opt [Simplify _Q_opt in parmest with block scenario structure. #3789]
• Merge multistart [[Depends on #3789] Implementing multistart version of theta_est using multiple sampling methods #3575]
• Adjust design based on feedback from reviews in dependent PRs
• Confirm testing passes on final design

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