chore: simplify calculate_next_run()

[waffensultan]

Description

Changes made:

• Replaced if/elif chain with match/case for clearer interval handling (Python 3.10+)
• Removed redundant weekday variable
• Simplified the monthly case by removing an unnecessary .replace(day=next_month.day) call, as the day will always be 1

Why:

• Code clarity and maintainability
• Eliminate redundant operations
• Make future modifications easier

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• DevOps / CI changes

How Has This Been Tested?

Eyeballed it

Test Configuration:

• Firmware version:
• Hardware:
• Toolchain:
• SDK:

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules