Salvages @Es1la's PR #13632 — a non-numeric timestamp in the persisted
feishu dedup state crashed adapter startup with ValueError/TypeError
from the unguarded float() call. Wrap the float() conversion in
try/except; skip the bad key and keep loading the rest.
The original PR also restructured existing TestDedupTTL tests to use
tempfile.TemporaryDirectory + HERMES_HOME patching — that was
test-hygiene scope creep unrelated to the bug. Kept only the
malformed-timestamp fix and added a focused regression test.