fix: remove window.Buffer assignment

[lenkan]

Previously, we've had a polyfill setting window.Buffer = import("buffer").Buffer. However, window is not available in all environments (e.g. service workers). This causes background browser extension workers to either fail or require an extra polyfill.

This PR fixes that by removing the polyfill and importing the module where it is needed instead.

There should be a way to ensure that the typescript build or eslint check fails if we are using APIs that are not available in both browser and node.js environment, but I haven't been able to figure it out yet.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (cedee3a) 82.86% compared to head (b9b1029) 82.86%.

Additional details and impacted files

@@             Coverage Diff              @@
##           development     #214   +/-   ##
============================================
  Coverage        82.86%   82.86%           
============================================
  Files               47       46    -1     
  Lines             4190     4190           
  Branches          1044     1044           
============================================
  Hits              3472     3472           
  Misses             689      689           
  Partials            29       29           

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