fix(streams/unstable): use relative path for in-package import

[kt3k]

It looks like JSR is unhappy with the specifier @std/streams/unstable-to-byte-stream in streams/unstable_capped_delimiter_stream.ts (probably because it is jsr: specifier referencing in-package path)

This PR tries to avoid the error above by using a relative path.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.15%. Comparing base (dcfb5b3) to head (135bb7a).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6909   +/-   ##
=======================================
  Coverage   94.14%   94.15%           
=======================================
  Files         583      583           
  Lines       42806    42806           
  Branches     6815     6815           
=======================================
+ Hits        40301    40302    +1     
+ Misses       2455     2454    -1     
  Partials       50       50           

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[dsherret]

LGTM