improve watcher update performance

[sokra]

measurements show a 13x improvement

[codecov]

Codecov Report

Merging #208 (dec2905) into main (0d90321) will decrease coverage by 0.53%.
The diff coverage is 86.84%.

@@            Coverage Diff             @@
##             main     #208      +/-   ##
==========================================
- Coverage   92.58%   92.05%   -0.54%     
==========================================
  Files           6        6              
  Lines        1039     1070      +31     
  Branches      246      258      +12     
==========================================
+ Hits          962      985      +23     
- Misses         77       85       +8     

Flag	Coverage Δ
integration	92.05% <86.84%> (-0.54%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
lib/watchpack.js	92.21% <86.84%> (-2.48%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 0d90321...dec2905. Read the comment docs.