HFI Calculator: Investigate Fuel Type C4

**Describe the task**
For C4 HFI and CFB are sometimes very different from REDapp, with CFB sometimes being calculated as 0.

**Acceptance Criteria**
- [ ] Establish reason for large discrepancy between REDapp CFB (using ros_t) and FireBAT (using ros_t)
- [ ] Resolve discrepancy if possible.

**Additional context**
Per DH and sample FBAs: C3, C5, C7, O1a/b are most commonly used to generate FBAs.
-- Plus: M2 (Coast FC, occasional) and S1-3 slash (referenced in Cariboo FBA).

Start by reproducing the C4 HFI and CFB calculations using ros_t in both REDapp and FireBAT, then compare the inputs and outputs. The work is done when the reason for the discrepancy, including cases where CFB is zero, is established and the discrepancy is resolved if possible.

Written by the indexing model from the issue text.