test(cache): number remote cache blobs and corrupt them through the backend

[wan9chi]

Motivation

Cases referred to blobs through the file backend's storage. Its blob IDs were sequential, and corrupt_archive overwrote remote-cache/blobs/1 directly. The public cache service from #718 stores blobs in R2 under random IDs, so those cases couldn't run against it.

Changes

• The tap numbers blobs in upload order in the request lines, e.g. GET /blob/1 200.
• remote-cache-server corrupt-blob NUMBER overwrites a stored blob through the backend. corrupt_archive uses it.
• The file backend uses random UUIDs as blob IDs, as the service does, so the numbering is already exercised here.

The only snapshot change is corrupt_archive's command line.

Stacked on #807.

🤖 Generated with Claude Code

[github-actions]

fspy benchmark

linux

dynamic/launch             change  +0.27%  [ -7.44% ..  +7.66%]  overhead  +284.18%
dynamic/access             change  -0.15%  [ -1.33% ..  +1.20%]  overhead   +14.36%
dynamic/access-relative    change  -0.12%  [ -5.62% ..  +4.34%]  overhead   +59.75%
dynamic/access-contended   change  +1.90%  [ -8.54% .. +18.03%]  overhead   +25.42%
static/launch              change  +0.10%  [ -7.64% ..  +8.24%]  overhead  +718.09%
static/access              change  -1.35%  [-16.76% .. +11.94%]  overhead  +823.04%
static/access-relative     change  +0.89%  [ -3.68% ..  +7.07%]  overhead +1215.01%
static/access-contended    change  -1.92%  [-13.73% ..  +9.79%]  overhead +2291.01%

macos

dynamic/launch             change  +0.47%  [ -3.45% ..  +6.82%]  overhead  +247.77%
dynamic/access             change  +0.00%  [ -7.76% ..  +5.62%]  overhead    +2.36%
dynamic/access-relative    change  -0.72%  [ -5.54% ..  +5.99%]  overhead  +252.64%
dynamic/access-contended   change  +1.03%  [-25.56% .. +63.00%]  overhead    -2.09%

windows

dynamic/launch             change  +0.01%  [ -3.57% ..  +3.87%]  overhead   +23.46%
dynamic/access             change  +0.35%  [ -3.11% .. +16.01%]  overhead    +2.51%
dynamic/access-relative    change  +0.00%  [ -7.29% ..  +2.08%]  overhead    +2.21%
dynamic/access-contended   change  +0.00%  [ -1.64% ..  +2.73%]  overhead    +1.69%