When a per-file pytest subprocess dies by signal (the sqlite cross-thread
close in #113186 was a SIGSEGV after every test had passed), faulthandler
prints "Fatal Python error: Segmentation fault" and no summary line, so
every count parses to 0. The runner filed that under "1 file where no
tests ran (collection/import error, ...)" beneath a summary that read
"0 failed" and exited 1 — two wrong diagnoses for one real bug, and it
was misread as a runner problem twice on main.
The runner now detects a signal death or a "Fatal Python error:" banner,
prefixes the captured output with the diagnosis (same convention as the
timeout path), marks the progress line CRASHED, counts "N files CRASHED"
on the summary line, lists the file in its own failure bucket, and no
longer trips the "NO TESTS RAN" guard for a crash that ran tests. The
flake retry already covers crashes (any non-zero rc), so nothing changes
there.
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