fix(p3-shim): avoid flakiness in http test

[vados-cosmonic]

The HTTP tests seem to cause some flakiness, so let's randomize the ports to avoid collisions first.

 ⎯⎯⎯⎯⎯⎯ Unhandled Errors ⎯⎯⎯⎯⎯⎯

Vitest caught 1 unhandled error during the test run.
This might cause false positive tests. Resolve unhandled errors to make sure your tests are not affected.

⎯⎯⎯⎯⎯ Uncaught Exception ⎯⎯⎯⎯⎯
Error: read ECONNRESET
 ❯ TCP.onStreamRead node:internal/stream_base_commons:218:20

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Serialized Error: { errno: -104, code: 'ECONNRESET', syscall: 'read' }
This error originated in "test/http.test.js" test file. It doesn't mean the error was thrown inside the file itself, but while it was running.
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Likely the fix will be to add retries to the specific test that's failing, but since there's no obvious source, this refactor reduces the likelihood and if the flakes reappear we can drill down to the relevant test and add retries in case network is flaky (though localhost really should not be).