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/egraph.cpp

@@ -116,12 +116,12 @@ static void test3() {
     g.merge(nx,  nz, justifications + 2);
     g.merge(nx,  nu, justifications + 3);
     g.propagate();
-    SASSERT(!g.inconsistent());
+    ENSURE(!g.inconsistent());
     g.merge(nx, ny, justifications + 4);
     std::cout << g << "\n";
     g.propagate();
     std::cout << g << "\n";
-    SASSERT(g.inconsistent());
+    ENSURE(g.inconsistent());
     ptr_vector<int> js;
     g.begin_explain();
     g.explain<int>(js, nullptr);