Add expense shock calibration(s)

[mnwhite]

The first commit adds a new income process constructor that incorporates Mateo's seven point medical expense shock distribution (by five year age blocks), from his JMP. HS and college specifications are tested. His approach specifies medical expenses as negative transitory income shocks.

The next commit will add Fulford and Low's estimation result from the earlier version of their paper, which uses PrefShockConsumerType or KinkyPrefConsumerType MedShockConsumerType.

[mnwhite]

This PR is meant to address #1500

[Copilot]

Pull request overview

Adds calibration support for expense/medical shocks by introducing a new income-process constructor that treats medical expenses as negative transitory income shocks (Velasquez-Giraldo 7-point-by-age-block spec), and aligns MedShock model outputs/tests/docs to use MedLvl.

Changes:

• Add construct_lognormal_income_process_with_mvg_medical_expenses and tests validating the expanded transitory shock support size by age.
• Update MedShock model tracking/control naming from Med to MedLvl across code, tests, and example notebook.
• Introduce a Fulford_and_Low_params parameter dictionary and document changes in the changelog.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
tests/ConsumptionSaving/test_modelInits.py	Adds tests exercising the new MVG medical-expense income process constructor.
tests/ConsumptionSaving/test_ConsMedModel.py	Updates simulation tracking key from Med to MedLvl.
examples/ConsMedModel/MedShockConsumerType.ipynb	Updates tracked variable and plotting to use MedLvl.
docs/CHANGELOG.md	Notes the new constructor and related updates.
HARK/models/ConsMedShock.yaml	Updates policy function naming/call signature to return (cLvl, MedLvl, xLvl).
HARK/ConsumptionSaving/ConsMedModel.py	Adds zero-probability support for MedShk discretization, introduces Fulford & Low params, and renames tracked med variable to MedLvl.
HARK/Calibration/Income/IncomeProcesses.py	Adds MVG medical-expense income process constructor (expense shocks as negative transitory income).

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.