Description

Add a classify_using_Hessian function that can assess the identifiability of an optimisation result and return an informative message to the user.

Issue reference

Fixes #362.

Review

Before you mark your PR as ready for review, please ensure that you've considered the following:

• Updated the CHANGELOG.md in reverse chronological order (newest at the top) with a concise description of the changes, including the PR number.
• Noted any breaking changes, including details on how it might impact existing functionality.

Type of change

• New Feature: A non-breaking change that adds new functionality.
• Optimization: A code change that improves performance.
• Examples: A change to existing or additional examples.
• Bug Fix: A non-breaking change that addresses an issue.
• Documentation: Updates to documentation or new documentation for new features.
• Refactoring: Non-functional changes that improve the codebase.
• Style: Non-functional changes related to code style (formatting, naming, etc).
• Testing: Additional tests to improve coverage or confirm functionality.
• Other: (Insert description of change)

Key checklist:

• No style issues: $ pre-commit run (or $ nox -s pre-commit) (see CONTRIBUTING.md for how to set this up to run automatically when committing locally, in just two lines of code)
• All unit tests pass: $ nox -s tests
• The documentation builds: $ nox -s doctest

You can run integration tests, unit tests, and doctests together at once, using $ nox -s quick.

Further checks:

• Code is well-commented, especially in complex or unclear areas.
• Added tests that prove my fix is effective or that my feature works.
• Checked that coverage remains or improves, and added tests if necessary to maintain or increase coverage.

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