chore: improve browser support

[jeluard]

Motivation

Make sure lodestar libs (e.g. light-client) can be loaded in a browser without relying on nodejs shims.
Recent bundler push for not relying on those (e.g. esbuild and vite)

[codecov]

Codecov Report

Merging #6384 (8d88f43) into unstable (8e0078b) will decrease coverage by 0.01%.
Report is 1 commits behind head on unstable.
The diff coverage is n/a.

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable    #6384      +/-   ##
============================================
- Coverage     60.15%   60.15%   -0.01%     
============================================
  Files           407      407              
  Lines         46512    46508       -4     
  Branches       1550     1550              
============================================
- Hits          27981    27977       -4     
  Misses        18499    18499              
  Partials         32       32              

[wemeetagain]

Maybe we should add a linter rule that types should be imported with import type or import {type if possible.

[wemeetagain]

🎉 This PR is included in v1.16.0 🎉