SLA Calculations 1/2: Add unit tests to capture current behaviour

[valentijnscholten]

Adds some unit tests to capture current behaviour:

• to understand the calculation that does some magic with days remaining
• to make sure we don't regress in the future if we simplify the calculation, or add business days support.

[dryrunsecurity]

DryRun Security Summary

A new unit test file for SLA calculations in DefectDojo is added, with five test methods and a security finding related to potential information disclosure through logging configuration.

Expand for full summary

The PR introduces a new unit test file for SLA calculations in DefectDojo, implementing five test methods to validate various SLA scenarios. Security findings include: 1) Potential information disclosure risk from logging configuration if log levels are not properly set in production, as noted in the file's security analysis section.

View PR in the DryRun Dashboard.