fix(cli/unstable): speed up ProgressBarStream tests

[minato32]

Closes #6674.

ProgressBarStream() flushes and ProgressBarStream() cancels slept 500–1000ms between each of 10 chunks, so each test took ~5–10s — almost all of it idle. The sleeps don't gate the assertion: it only checks that the writable side ends with a newline (`0x0a`), which is emitted by bar.stop() regardless of how many interval ticks fired.

Drop the per-chunk delay to 5ms and override interval: 1 on the progress bar so the ticking path still exercises but doesn't dominate runtime. The two tests now run in ~110ms combined instead of ~15s.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.64%. Comparing base (f0431c2) to head (3da7c12).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7193   +/-   ##
=======================================
  Coverage   94.64%   94.64%           
=======================================
  Files         629      630    +1     
  Lines       51895    51898    +3     
  Branches     9373     9374    +1     
=======================================
+ Hits        49116    49119    +3     
  Misses       2211     2211           
  Partials      568      568           

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