Bound static-bin smoke tests with per-test timeout

[jserv]

Wrap every guest-binary invocation in timeout TEST_TIMEOUT (default 10s, override via env) so a regression that hangs a guest binary (futex deadlock, EPOLLET busy-loop, blocking syscall miswire) cannot stall "make check" indefinitely. Surface the GNU-timeout rc=124 as a distinct " (timeout)" failure instead of letting it fall through to the generic "pattern not found, rc=124" path; the two have different root causes (livelock vs. semantic regression) and deserve different signal in CI logs.

Fail upfront with a clear message when 'timeout' is missing from PATH, so an absent Homebrew coreutils install produces one error rather than every test reporting "command not found, rc=127".

Use integer compare on the rc check, and apply the wrapper uniformly across srun_check, srun_pipe, srun_script, and the two inlined diff cases.

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Summary by cubic

Add a per-test timeout to static-bin smoke tests to prevent hangs and make CI failures clearer. Default is 10s via TEST_TIMEOUT; timeouts are labeled explicitly and we fail fast if timeout is missing.

• Bug Fixes
  • Wrap all guest-binary runs with timeout using TEST_TIMEOUT (default 10s, override via env).
  • Treat exit code 124 as a distinct "(timeout)" failure.
  • Exit early with a clear error if timeout is not on PATH (e.g., missing Homebrew coreutils on macOS).
  • Apply uniformly to srun_check, srun_pipe, srun_script, and inline diff checks.
  • Use integer exit code comparisons.
  • Replace recursive factorial test with a simple sum; expected output now result=15.

^{Written for commit f0e021e. Summary will update on new commits.}

[cubic-dev-ai]

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