gh-154194: Do not fail the whole sample in Tachyon if we can degrade

[maurycy]

As always, see #154194 for the context. Shortly: right now remote inspection fails the whole sample when it hits the limits (and we're really not sure what are the best limits) OR always when reading a part fails. This is too strict, wasteful and introduces scary bias, as observed in https://discuss.python.org/t/tachyon-97-error-rate/107619.

The PR introduces graceful degradation with the sentinels like <unreadable frame> (funcname), <unknown function> (funcname), <unknown file> (filename) and the (len=N) suffix if we hit the cap. Also, it introduces MAX_REMOTE_READ as a safety check, and attemps to better differentiate between transient failures in _Py_RemoteDebug_IsFatalReadError().

Importantly: degraded frames are never cached, while the truncated strigs are cached.

Fixes #154194

• Issue: _remote_debugging: Degrade gracefully reads instead of failing the whole read completely #154194

[maurycy]

I believe that the CI failures are caused by the fact that test_async_aware_running_sees_only_cpu_task does not terminate. It worked only because a torn read caused an exception. That's what inspired #153365 in the first place.