TPTP frontend: fix TFF numeric atom typing, decimal literals, and $uminus (#9518)

This PR targets the main TFF frontend parsing failures: bare numeric
atoms were being treated as uninterpreted terms (`U`) in formula
position, decimal literals were not parsed, and `$uminus` was not
recognized as an arithmetic builtin. These issues caused widespread
parse/type failures in arithmetic-heavy TPTP inputs.

- **Numeric atom parsing in formulas (TFF)**
- Added a shared numeric-literal parser path for term/formula contexts.
- In atomic formulas, numeric LHS now parses as arithmetic numerals
before `=`/`!=` handling, avoiding `U` vs `Int/Real` mismatches.

- **Decimal literal support**
- Extended numeral parsing to accept `d.d` forms and construct `Real`
numerals.
- Keeps existing integer (`d`) and rational (`d/d`) behavior on the same
code path.

- **`$uminus` builtin support**
  - Added explicit handling for `$uminus(<arg>)` in term parsing.
- Enforces arity 1 and arithmetic-argument checks; maps directly to
arithmetic unary minus.

- **Focused regression coverage**
  - Added/updated TPTP unit cases for:
    - bare integer inequality: `31 != 12`
    - decimal arithmetic literal usage
    - `$uminus` in arithmetic predicates

Example of now-supported inputs:

```tptp
tff(c1,conjecture, 31 != 12).
tff(c2,conjecture, ~ $less(-3.25,-8.69)).
tff(c3,conjecture, $less($uminus(2),0)).
```

---------

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

@@ -81,6 +81,15 @@ R"(tff(c1,conjecture, ? [X: $int] : $less(12,X)).)",
          "% SZS status Theorem"},
         {"tff-lesseq-built-in",
 R"(tff(c1,conjecture, $lesseq(2,2)).)",
+         "% SZS status Theorem"},
+        {"tff-bare-integer-equality",
+R"(tff(c1,conjecture, 31 != 12).)",
+         "% SZS status Theorem"},
+        {"tff-decimal-literal",
+R"(tff(c1,conjecture, ~ $less(-3.25,-8.69)).)",
+         "% SZS status Theorem"},
+        {"tff-uminus-built-in",
+R"(tff(c1,conjecture, $less($uminus(2),0)).)",
          "% SZS status Theorem"}
     };
     for (auto const& c : cases) {