opt: validate strict optimization optima faithfully with delta-rational bounds (#10059)

## Problem

Maximizing/minimizing under a **strict** inequality has a delta-rational
optimum. For

```smt2
(declare-const r Real)
(assert (< r 1))
(maximize r)
(check-sat)
(get-objectives)
```

the optimum is the supremum `1 - epsilon`, but z3 reported `r = 0`.

The same defect makes shared-symbol objectives report a value matching
**neither the model nor the true optimum** (issue #10028 follow-up).
Minimal reproducer — a 6-mark Golomb ruler (a `>32`-arg `distinct`, so
the objective is coupled to EUF) with a strict real objective `obj >
x5`, whose true optimum is `17 + epsilon`:

| case | before | after |
|---|---|---|
| `maximize r`, `r < 1` | `0` ❌ | `1 - epsilon` ✅ |
| `minimize r`, `r > 1` | `0` ❌ | `1 + epsilon` ✅ |
| Golomb `minimize obj`, `obj > x5` | `35/2` / `7+eps` ❌ | `17 +
epsilon` ✅ |

## Root cause

`check_bound` validates the LP hint by asserting `objective >= optimum`.
For a supremum `1 - epsilon` this is a **lower** bound whose value
carries a **negative** infinitesimal `(1, -1)`.

No `lconstraint_kind` can express that. The kind->infinitesimal map only
yields the *matching-sign* cases — `GT` -> lower `(r, +1)`, `LT` ->
upper `(r, -1)` — or zero (`GE`/`LE`). The opposite-sign lower bound
`(r, -1)` (i.e. `r >= r0 - delta`) is a *relaxation* that no strict
inequality produces. `opt_solver::mk_ge` therefore projected the
`-epsilon` away, turning `r >= 1 - epsilon` into the over-strong,
unsatisfiable `r >= 1`; validation failed and the strictly smaller
current model value was reported instead.

## Fix — carry the infinitesimal faithfully through the bound pipeline

- **`lp_api::bound`** gains an `eps` component so `get_value` returns
the true delta value (no spurious rational fixed-variable equality is
propagated to EUF).
- **`lar_base_constraint`** stores its right-hand side as a
delta-rational `impq` pair; `rhs()` returns the rational component,
`bound_eps()` the infinitesimal one.
- **`lar_solver`** bound activation/update threads the whole `impq`
bound, so a lower bound `(r, -1)` can be asserted. `constraint_holds`
accounts for it using the **same** strict-bounds delta that flattens the
model, computed **once per model**.
- **`theory_lra::mk_ge`** builds a *fresh* predicate for the `(r, -1)`
lower bound (to avoid colliding with an already-internalized `v >= r`
literal) and attaches `eps = -1`. **`opt_solver::mk_ge`** passes the
unprojected value to `theory_lra` / `theory_mi_arith` /
`theory_inf_arith` (whose bounds are already `inf_rational`).

The pair machinery is what makes the supremum both representable
(optimum `1 - epsilon`) and validatable; the reported witness model
remains the flattened rational (`find_delta_for_strict_bounds`),
consistent with the existing epsilon semantics.

## Validation

- Strict optima correct: `1-eps`, `1+eps`, bounded `2<r<5 -> 5-eps`, and
lex/box variants.
- Integer optima and the #10028 shared-symbol cases unchanged (Golomb
n=6/7/8 -> 17/25/34, consistent with the model).
- Unit tests **92/92** (release); no new debug-suite failures.
- Opt regression corpus (73 files, `model_validate=true`)
**byte-identical** to baseline.

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

---------

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

.github/workflows/ocaml.yaml

@@ -28,21 +28,13 @@ jobs:
           restore-keys: |
             ${{ runner.os }}-ccache-
 
-      # Cache opam (compiler + packages)
-      - name: Cache opam
-        uses: actions/cache@v6.1.0
-        with:
-          path: ~/.opam
-          key: ${{ runner.os }}-opam-${{ matrix.ocaml-version }}-${{ github.sha }}
-          restore-keys: |
-            ${{ runner.os }}-opam-${{ matrix.ocaml-version }}-
-
-      # Setup OCaml via action
+      # Setup OCaml via action (handles opam caching internally)
       - uses: ocaml/setup-ocaml@v3
         with:
           ocaml-compiler: ${{ matrix.ocaml-version }}
           opam-disable-sandboxing: true
-          
+          cache-prefix: v1
+
       # Platform-specific dependencies
       - name: Install system dependencies (Ubuntu)
         if: matrix.os == 'ubuntu-latest'
@@ -123,4 +115,4 @@ jobs:
       - name: Run ml_example (native)
         run: |
           export DYLD_LIBRARY_PATH=$(pwd)/build
-          ./ml_example
+          ./ml_example