test(server): Fix flaky test_bandwidth_burst_tolerance

[jan-auer]

The test left only 500ms of margin between the accumulated bandwidth debt and the burst tolerance, so a slow runner would see the debt drain back under the burst and admit the request that should have been rejected. Scaled the rate and burst down so the margin is seconds instead of milliseconds, keeping the same scenario.

Closes FS-459

[linear-code]

FS-459

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.71%. Comparing base (181df0a) to head (705f812).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #578      +/-   ##
==========================================
+ Coverage   87.64%   87.71%   +0.06%     
==========================================
  Files          94       94              
  Lines       15425    15505      +80     
==========================================
+ Hits        13520    13600      +80     
  Misses       1905     1905              

Components	Coverage Δ
Rust Backend	92.41% <ø> (+0.05%)	⬆️
Rust Client	79.89% <ø> (ø)
Python Client	90.90% <ø> (ø)

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