Initialize prescribed fire site-level variables

[glemieux]

Addresses issue #1470

Description:

This initializes rxfire_area_fi and rxfire_area_fuel` which are currently uninitialized on the main branch.

Collaborators:

@samsrabin @XiulinGao @mvdebolskiy

Expectation of Answer Changes:

None, should be B4B

Description of generative AI usage (as necessary)

No AI usage

Checklist

If this is your first time contributing, please read the CONTRIBUTING document.

All checklist items must be checked to enable merging this pull request:

Contributor

• The in-code documentation has been updated with descriptive comments
• The documentation has been assessed to determine if updates are necessary
• Describe use of generative AI (if necessary)

Integrator

• FATES PASS/FAIL regression tests were run
• Evaluation of test results for answer changes was performed and results provided
• FATES-CLM6 Code Freeze: satellite phenology regression tests are b4b

If satellite phenology regressions are not b4b, please hold merge and notify the FATES development team.

Documentation

• Technical Note update:
• User's Guide update:

Test Results:

CTSM (or) E3SM (specify which) test hash-tag:

CTSM (or) E3SM (specify which) baseline hash-tag:

FATES baseline hash-tag:

Test Output:

[samsrabin]

Looks good, thanks—but looking at #1470, what about rxfire_area_final?