Ramon benchmark for Z3
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Job description: 
Job tag: smt_qflia-threads-4-smts_bugfix2
Runner: rise-runner-2
Z3 repo: ilanashapiro/z3
Z3 commit: dec2f2ec9953182d57d1c6a8a776c713e3b64bf2
Z3 branch: smts_tree_algorithms_bugfix
Z3 options: "-T:60 -v:0 smt.threads=4 tactic.default_tactic=smt smt.auto_config=false"
Z3 inputs: inputs/QF_LIA
Z3 commit message: fix bug about backtracking condition being too strict: The epoch guard should not block backtrack(...) the same way it blocks try_split(...). A stale worker that proves UNSAT for n should still be able to
  close n, and that closure should then cancel the other workers on n and its subtree.

  I changed smt/smt_parallel.cpp accordingly:

  - try_split(...) still uses epoch to reject stale structural splits
  - backtrack(...) no longer requires is_lease_valid(..., epoch); it only requires that the lease is not already canceled

  So the intended asymmetry is now restored:

  - stale split: reject
  - stale unsat/backtrack: allow closure, then cancel affected workers
