test: replace SASSERT with ENSURE, remove Windows-only guards (#10086)

Unit tests relied on `SASSERT()` which is a no-op in release builds
(`DEBUG_CODE` wrapper), silently skipping all assertions outside debug
mode. Several test files were also gated behind `#ifdef _WINDOWS`,
making them dead code on Linux/macOS CI.

## Changes

- **`SASSERT` → `ENSURE` in 20 test files (200 occurrences)**: `ENSURE`
maps to `VERIFY` and always executes regardless of build type, ensuring
test assertions are active in both debug and release builds.

- **`src/test/diff_logic.cpp`**: Removed `#ifdef _WINDOWS` wrapping the
entire file. No Windows-specific APIs were used; the guard only
prevented compilation on non-Windows platforms.

- **`src/test/dl_product_relation.cpp`**: Removed `#ifdef _WINDOWS`
guard around `tst_dl_product_relation()`. The function body has no
platform dependencies.

- **`src/test/sat_local_search.cpp`**: Replaced `sscanf_s`
(MSVC-specific) with portable `sscanf`; added return-value check to
detect malformed input. Previously, `build_instance()` unconditionally
returned `false` on non-Windows, making the SAT local search test a
no-op on Linux/macOS.

---------

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

src/test/fuzzing/expr_delta.cpp

@@ -61,13 +61,13 @@ bool expr_delta::delta_dfs(unsigned& n, expr* e, expr_ref& result) {
     }
     else if (is_app(e)) {        
         if (m.is_bool(e)) {
-            SASSERT(n >= 2);
+            ENSURE(n >= 2);
             n -= 2;
         }
         return delta_dfs(n, to_app(e), result);
     }
     else if (is_quantifier(e)) {
-        SASSERT(n >= 2);
+        ENSURE(n >= 2);
         n -= 2;
         quantifier* q = to_quantifier(e);
         if (delta_dfs(n, q->get_expr(), result)) {

src/test/fuzzing/expr_rand.cpp

@@ -77,7 +77,7 @@ expr* expr_rand::choose_expr(sort* s) {
         if (!m_nodes.find(s, vals)) {
             UNREACHABLE();
         }
-        SASSERT(vals);
+        ENSURE(vals);
     }
     unsigned idx = m_random(vals->size());
     return (*vals)[idx].get();