Normalize the fuel_types table

**Describe the task**
Normalize the fuel_types table to allow for unique records for having nullable percent conifer, percent dead fir, and percent grass cure fields.

**Acceptance Criteria**
- [ ] Automatically derive specific criteria from the task description.
- [ ] Ensure the criteria are actionable and testable.
- [ ] Include any edge cases or special conditions mentioned in the description.

**Additional context**
- Add any other context about the task here.
- Or here

Start by locating the schema or migration that defines the fuel_types table and inspect its current uniqueness constraints and nullable fields. Determine how records with nullable percent conifer, percent dead fir, and percent grass cure values should be uniquely represented. Done means the table accepts the intended unique records and has tests or migration validation covering the nullable-field edge cases.

Written by the indexing model from the issue text.