Convert hfi_calc bdd tests

[dgboss]

• Convert hfi_calc fire_centres route tests from bdd to vanilla pytest
• closes #4025

  Test Links:

  Landing Page MoreCast Percentile Calculator C-Haines FireBat FireBat bookmark Auto Spatial Advisory (ASA) HFI Calculator

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 80.43%. Comparing base (8d58b59) to head (69387f0). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #4128 +/- ## ========================================== - Coverage 80.94% 80.43% -0.52% ========================================== Files 309 309 Lines 11876 11876 Branches 537 537 ========================================== - Hits 9613 9552 -61 + Misses 2145 2138 -7 - Partials 118 186 +68 ```

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