[3.14] gh-133885: Use locks instead of critical sections for _zstd (gh-134289) (gh-134560)

Move from using critical sections to locks for the (de)compression methods.
Since the methods allow other threads to run, we should use a lock rather
than a critical section.
(cherry picked from commit 8dbc11971974a725dc8a11c0dc65d8f6fcb4d902)

Co-authored-by: Emma Smith <emma@emmatyping.dev>