feat: better subscription period formatting on invoice

[nijel]

Proposed changes

Do not include it in description, include it as separate fields. This makes it also disappear from the payment info where the field is limited.

Checklist

• Lint and unit tests pass locally with my changes.
• I have added tests that prove my fix is effective or that my feature works.
• I have added documentation to describe my feature.
• I have squashed my commits into logic units.
• I have described the changes in the commit messages.

Other information

[codecov]

Codecov Report

Attention: Patch coverage is 86.66667% with 2 lines in your changes missing coverage. Please review.

Project coverage is 81.90%. Comparing base (34e3a05) to head (5b3c954).
Report is 16 commits behind head on main.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2324      +/-   ##
==========================================
- Coverage   81.90%   81.90%   -0.01%     
==========================================
  Files          39       39              
  Lines        3952     3963      +11     
  Branches      378      379       +1     
==========================================
+ Hits         3237     3246       +9     
- Misses        576      577       +1     
- Partials      139      140       +1