TPTP frontend: enforce implicit universal quantification for free variables and add regression coverage (#9527)

Discussion #9524 reported systematic TPTP result polarity errors
(notably `Unsatisfiable/Theorem` cases returned as `Satisfiable`) and
timeout-path instability in the frontend. The dominant issue was
semantic: free variables in FOF/CNF formulas were parsed as constants
instead of implicitly universally quantified variables.

- **Parser semantics: free variables now follow TPTP rules**
- In `/home/runner/work/z3/z3/src/cmd_context/tptp_frontend.cpp`, free
variables encountered while parsing an annotated formula are now
collected in formula scope and wrapped with a top-level `forall`.
- This applies to both term and atomic-formula paths, so variable
occurrences are treated consistently.
- Explicitly bound quantifier variables continue to take precedence over
implicit ones.

- **Scoped implementation cleanup**
- Added scoped state for implicit-variable collection to avoid leaking
parser state across formulas.
- Kept variable binding order stable so quantifier construction is
deterministic.

- **Timeout-path robustness**
- Updated frontend exception catches to `const&` in the TPTP stream
entrypoint to make timeout/error handling behavior consistent with
thrown exception forms.

- **Regression tests**
- Extended `/home/runner/work/z3/z3/src/test/tptp.cpp` with focused
cases for:
    - FOF free-variable implicit universal quantification.
    - CNF free-variable implicit universal quantification.

```tptp
cnf(c1,axiom, p(X)).
cnf(c2,axiom, ~ p(a)).
```

This now maps to `forall X. p(X)` plus `~p(a)`, yielding `% SZS status
Unsatisfiable` as expected.

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: NikolajBjorner <3085284+NikolajBjorner@users.noreply.github.com>

src/test/tptp.cpp

@@ -65,6 +65,14 @@ fof(c1,conjecture, mortal(socrates)).)",
         {"simple-sat",
 R"(fof(a1,axiom, p(a)).)",
          "% SZS status Satisfiable"},
+        {"fof-implicit-forall",
+R"(fof(a1,axiom, p(X)).
+fof(c1,conjecture, p(a)).)",
+         "% SZS status Theorem"},
+        {"cnf-implicit-forall",
+R"(cnf(c1,axiom, p(X)).
+cnf(c2,axiom, ~ p(a)).)",
+         "% SZS status Unsatisfiable"},
         {"tff-negative-literal",
 R"(tff(c1,conjecture, $less(-2,2)).)",
          "% SZS status Theorem"},