Fix Producer#close raising ThreadError when called from a signal trap…

… context (#867)

Puma's `after_stopped` DSL hook in single mode runs in a Ruby signal trap context.
Ruby forbids Mutex#synchronize from trap contexts and raises:
  ThreadError: can't be called from trap context

Producer#close calls @transaction_mutex.synchronize, which hits this restriction.

The fix rescues ThreadError at the method level and re-runs close in a background
thread, joining it so the caller blocks until the producer is fully closed. This
mirrors the existing pattern used to escape the fd-poller thread deadlock.

Closes #866

v2.10.0 (#859)

Update CHANGELOG.md

Signed-off-by: Maciej Mensfeld <maciej@mensfeld.pl>

v2.8.16 (#799)

fix release date

v2.8.14 (#724)

v2.8.13 (#715)

v2.8.12 (#705)

v2.8.11 (#698)

v2.8.10 (#693)