Episode Calculations

[eanders]

Merging this PR

• use the squash-merge strategy for PRs targeting main

Description

During the performance work on the enrollments roll-up a few issues were identified with the calcuation of "new episode". This attempts to fix:

• Lack of documentation
• Duplicate episode markers on duplicate enrollments
• Divergence from official the HUD definition

Type of change

• Bug fix

Checklist before requesting review

• I performed a self-review of my code
• I ran the OP review skill
• I ran the code that is being changed under ideal conditions, and it doesn't fail
• If adding a new endpoint / exposing data in a new way, I have:
  • ensured the API can't leak data from other data sources
  • ensured this does not introduce N+1s
  • ensured permissions and visibility checks are performed in the right places
• Any major architectural changes are supported by an approved ADR (Architectural Decision Record)
• I updated the documentation (or not applicable)
• I added spec tests (or not applicable)
• I provided testing instructions in this PR or the related issue (or not applicable)