refactor: resolve eslint warnings (max-depth, complexity) - src/lib/mutate-processor.ts

[btlghrants]

Describe what should be investigated or refactored

Refactor of src/lib/mutate-processor.ts to reduce complexity warnings:

/pepr/src/lib/mutate-processor.ts
  18:8  warning  Async function 'mutateProcessor' has a complexity of 18. Maximum allowed is 10        complexity
  18:8  warning  Async function 'mutateProcessor' has too many statements (49). Maximum allowed is 20  max-statements
  99:9  warning  Blocks are nested too deeply (4). Maximum allowed is 3                                max-depth

Additional context

Fixes #1532
In support of #1248

[codecov]

Codecov Report

Attention: Patch coverage is 71.42857% with 20 lines in your changes missing coverage. Please review.

Project coverage is 80.28%. Comparing base (46c8514) to head (c99dfbc).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/lib/mutate-processor.ts	71.42%	17 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1543      +/-   ##
==========================================
+ Coverage   78.24%   80.28%   +2.04%     
==========================================
  Files          41       41              
  Lines        1889     1902      +13     
  Branches      444      436       -8     
==========================================
+ Hits         1478     1527      +49     
+ Misses        409      346      -63     
- Partials        2       29      +27     

Files with missing lines	Coverage Δ
src/lib/mutate-processor.ts	62.63% <71.42%> (+52.38%)	⬆️

... and 7 files with indirect coverage changes

[btlghrants]

Was able to squash the complexity and max-depth warnings but was only able to reduce the max-statements down to 25 (from 49); going any lower on the max-statements will have undesirable consequences on the cohesiveness of this method, IMO, so I added an eslint comment to extend the upper limit appropriately.

[samayer12]

Related to #1547

[samayer12]

We did a sync review of changes, good to go.