fix: faster direct read approach

[jimmywarting]

This will saves some memory and make decoding responses faster and avoids some unnecessary overhead that needs to clone the hole body using Blob that in turns requires everything to be immutable and requires a lots of data being copied.

using body.text() became like 2x faster, compared to the prev commit 👍

closes #1533

[codecov-commenter]

Codecov Report

Merging #1537 (c358cbd) into main (aa8782c) will increase coverage by 0.00%.
The diff coverage is 97.36%.

@@           Coverage Diff           @@
##             main    #1537   +/-   ##
=======================================
  Coverage   94.90%   94.90%           
=======================================
  Files          50       50           
  Lines        4609     4632   +23     
=======================================
+ Hits         4374     4396   +22     
- Misses        235      236    +1     

Impacted Files	Coverage Δ
lib/fetch/body.js	98.73% <97.36%> (+0.21%)	⬆️
lib/fetch/file.js	91.66% <0.00%> (-1.20%)	⬇️

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[mcollina]

lgtm