chore: add return types to watch-processor.ts

[samayer12]

Description

Adds return typing to untyped functions.

Related Issue

Fixes #1546

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 78.82%. Comparing base (a7989f7) to head (e99231e).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1562   +/-   ##
=======================================
  Coverage   78.82%   78.82%           
=======================================
  Files          41       41           
  Lines        1804     1804           
  Branches      403      430   +27     
=======================================
  Hits         1422     1422           
  Misses        380      380           
  Partials        2        2           

Files with missing lines	Coverage Δ
src/lib/watch-processor.ts	78.64% <100.00%> (ø)