HFI Calculator (and all Fire Behaviour Tools): Fuel types C7b (C3m, BL)

_This was originally written in context of Fire Behaviour Calculator work, summer 2021 - our understanding of unofficial fuels has evolved over the following months. This impacts most/all of our products._

**Original Context:**
Some fire centres use a C7b "fuel type". It's not an official fuel type, but rather a proposal to merge the C7 fuel type with a grass type. There is insufficient empirical evidence to support this as an actual fuel type and it's use could result in liability issues.

**DECISIONS**
- C7b: incorporate into HFI #1637
- C3m (NW, SE) - use C3 in interim - spun off into #1659
- BL (Coastal) - use c5 in interim - spun off into #1658

**Goal**
- official equation, not spreadsheets, our code will become a standard

**Options**
**1.** Implement the C7b calculations in FireBAT and HFI Calculator.
**2.** Don't implement it.

**Context**
- not implementing will block adoption of our tools
- C7 fuel assumes 100% grass curing - in Kamloops and Southeast FCs in particular this produces indices and calculations that don't reflect reality, resulting in inaccurate Advisories or Prep Levels
- C7b allows them to adjust grass curing throughout the season (less than 100%)
- Although unofficial, it is in use now widely, evidenced in FBAs and HFI Workbooks in several FCs
- DP at National level is investigating, DH is collaborating
- [C7b Spreadsheet](https://teams.microsoft.com/l/file/573310E4-CE24-4862-988D-0C81C86E1BDC?tenantId=6fdb5200-3d0d-4a8a-b036-d3685e359adc&fileType=xls&objectUrl=https%3A%2F%2Fbcgov.sharepoint.com%2Fteams%2F01324%2FShared%20Documents%2FGeneral%2FUX%2FFireBAT%20MVP%2FSoutheast%20FC%2FNewC7b%20-%20C7%20with%20curing3.xls&baseUrl=https%3A%2F%2Fbcgov.sharepoint.com%2Fteams%2F01324&serviceName=teams&threadId=19:61ee3cf6291249ef849064eb2748c6e7@thread.tacv2&groupId=23431815-15c2-4928-9839-d8878e46b956)

Review the C7b decisions in this issue and the follow-up issues #1637, #1659, and #1658, then compare the linked C7b spreadsheet with the current FireBAT and HFI Calculator behavior. Confirm the approved scope and acceptance criteria before implementation; this issue is done only when that scope is agreed and the affected tools reflect it.

Written by the indexing model from the issue text.