chore: return types on schedule

[cmwylie19]

Description

Adds return types to schedule to unify typing

Related Issue

Fixes #1454

Relates to #

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Other (security config, docs update, etc)

Checklist before merging

• Unit, Journey, E2E Tests, docs, adr added or updated as needed
• Contributor Guide Steps followed

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.12%. Comparing base (b74496c) to head (81a36ef).
Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1505   +/-   ##
=======================================
  Coverage   79.12%   79.12%           
=======================================
  Files          39       39           
  Lines        1720     1720           
  Branches      404      388   -16     
=======================================
  Hits         1361     1361           
- Misses        330      357   +27     
+ Partials       29        2   -27     

Files with missing lines	Coverage Δ
src/lib/schedule.ts	100.00% <100.00%> (ø)

... and 7 files with indirect coverage changes

[btlghrants]

Yep, straight-forward return type adds.