ci: add timeouts and fail-fast guards to the workflows - #549

Address review findings on the fail-fast change:

- Guards now read `success() && !cancelled() && steps.<prev>.outcome ==
  'success'`. A bare `!cancelled()` suppresses GitHub's implicit `success()`
  check, so a failure in a step outside the immediate chain would not have
  stopped later steps.
- A step that already carries a condition of our exact shape gets it replaced
  in place instead of gaining a second `if:` key, which is invalid workflow
  syntax. Steps whose condition is anything else (matrix picks, failure
  reporters such as `steps.x.outcome != 'success'`) keep it and stay out of
  the chain.
- Jobs that call a reusable workflow no longer get `timeout-minutes:` (GitHub
  forbids it there); the timeouts live on the jobs inside the called
  workflows instead.

The four guards this branch added were no-ops. GitHub applies a default
`success()` check to a step unless the `if` names a status function, and
`success()` means every earlier step succeeded, so
`success() && !cancelled() && steps.X.outcome == 'success'` can never be false
for an `X` that already ran. Each guard, and the `id:` it read, is gone.

What actually stops a wedged step is a budget, and there was one only on the two
`-prod` runs. Every step now carries its own `timeout-minutes`, sized well above
a healthy run: a checkout that hangs on the network fails in ten minutes, and a
build or a test that wedges fails at its own budget instead of spending the rest
of the job's hour on it. The job-level 60 stays as a backstop that should never
fire first.

Windows also ran `-prod` without `VLS_VLANG_V_REPO`, which `index_test.v` and
`integration_test.v` read to find the vlang/v checkout; without it those tests
resolve `vlib` from the installed V while the ubuntu `-prod` run used the
checkout, so the two covered different trees. Both now set it.

Checked with actionlint 1.7.12 (0 errors). The Windows and macOS jobs are
currently red before vls is ever compiled, failing inside vlang/v's own build
(`Backend compiler error`, `Compilation of v.c failed`), which this cannot fix.