tptp: share 0-arity decls across sorts to fix bare constant equality (#9587)

Fix the TPTP frontend so that a bare name used in an equality refers to
a single shared `func_decl`, regardless of how the surrounding context
coerces its sort.

## Problem

With the following input the conjecture was not proved:

```tptp
fof(a1,axiom, ! [X] : (X = a)).
fof(c1,conjecture, b = a).
```

`parse_atomic_formula` created bare names as 0-arity **Bool
predicates**, and `coerce_eq` later retyped them by calling
`m.mk_func_decl(...)` directly, without registering the result in
`m_decls`. So the `a` used inside `! [X] : (X = a)` (coerced to sort
`U`) and the `a` used inside `b = a` (left as Bool) ended up as two
unrelated `func_decl`s sharing only the name. The axiom no longer
constrained the conjecture.

## Fix

In `src/cmd_context/tptp_frontend.cpp`:

1. Add `mk_zero_arity_decl(name, range)` / `coerce_zero_arity(app*,
range)` helpers that memoize the 0-arity `func_decl` per `(name, target
sort)` in `m_decls`, delegating to the existing `mk_decl_or_ho_const`
for `U` and Bool targets.
2. Rewrite `coerce_eq` to use the new helpers and add an explicit Bool /
non-Bool retyping branch so a bare-Bool side is recast to the other
side's sort.
3. In `parse_atomic_formula`, when a bare name is immediately followed
by `=` or `!=`, create it as a non-predicate (sort `U`). Terms in
equalities are no longer first introduced as Bool predicates.
4. Reorder the constructor init-list so `m_univ` is initialized before
the pinned ref vectors (matches declaration order; silences
`-Wreorder`).

Net effect: every reference to a given name at a given sort yields the
same `func_decl`, eliminating duplicate-symbol bugs in equalities over
bare TPTP constants.

## Test

Added `fof-bare-constant-equality` to `src/test/tptp.cpp`. Without the
C++ change the new case asserts; with it, `./build/release/test-z3 /seq
tptp` reports `PASS`.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/test/tptp.cpp

@@ -73,6 +73,10 @@ fof(c1,conjecture, p(a)).)",
 R"(cnf(c1,axiom, p(X)).
 cnf(c2,axiom, ~ p(a)).)",
          "% SZS status Unsatisfiable"},
+        {"fof-bare-constant-equality",
+R"(fof(a1,axiom, ! [X] : (X = a)).
+fof(c1,conjecture, b = a).)",
+         "% SZS status Theorem"},
         {"tff-negative-literal",
 R"(tff(c1,conjecture, $less(-2,2)).)",
          "% SZS status Theorem"},