[3.14] gh-142183: Cache one datachunk per tstate to prevent alloc/dealloc thrashing (GH-145789) (#145828)

Cache one datachunk per tstate to prevent alloc/dealloc thrashing when repeatedly hitting the same call depth at exactly the wrong boundary.

Move new _ts member to the end to not mess up remote debuggers' ideas of the
struct's layout. (The struct is only created by the runtime, and the new
field only used by the runtime, so it should be safe.)

(cherry picked from commit 706fd4ec08acbf1b1def3630017ebe55d224adfa)
Co-authored-by: T. Wouters <thomas@python.org>
Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>