server : test script : add timeout for all requests

[ngxson]

Some steps in server test script are missing timeout config, which make it to use the default value of 300 seconds

This causes the the CI to randomly (and rarely) fail. Mostly due to the instability of hosted runner:

• https://github.com/ggerganov/llama.cpp/actions/runs/10413617309/job/28841286271
• https://github.com/ggerganov/llama.cpp/actions/runs/10463963039/job/28976795340
• https://github.com/ggerganov/llama.cpp/actions/runs/10669606710/job/29571902646

This PR add timeout everywhere in the script, the value is 600 seconds, which is double the default value.

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[ngxson]

Small note: I tested the stability of CI by re-running test multiple times (mixed between slow and default test configs).

In rare occasion, windows test failed due to ERROR: Server stopped listening. After more careful inspections, I believe that the problem comes from race condition inside the test script itself. Since it rarely happens and is windows-only, I won't go deeper right now (i.e. won't fix)