🐛 Ensure that different formats with the same start fence are treated as distinct formats

[joshjennings98]

Description

Ensure that different formats with the same start fence are treated as distinct formats

the old parser would:

1. see ---
2. pick the first --- format
3. look only for closing ---
4. hit EOF / fail
5. report not found if it had a different end

This will still fallback to one the first parser (like it did before) if you have formats that aren't compatible e.g.:

Start: "---", End: "---", include delimiters false
Start: "---", End: "---", include delimiters true

Test Coverage

• This change is covered by existing or additional automated tests.
• Manual testing has been performed (and evidence provided) as automated testing was not feasible.
• Additional tests are not required for this change (e.g. documentation update).