fix: compare paths as path objects not strings (Windows backslash compat)

Author: Sunrisepeak

tests/unit/test_bmi_cache.cpp

@@ -45,8 +45,8 @@ void writeFile(const std::filesystem::path& p, std::string_view body) {
 
 TEST(BmiCache, KeyDirLayoutMatchesDocs26) {
     auto k = makeKey("/home/u/.mcpp");
-    EXPECT_EQ(k.dir().string(),
-              "/home/u/.mcpp/bmi/deadbeef0123abcd/deps/mcpplibs/mcpplibs.cmdline@0.0.1");
+    auto expected = std::filesystem::path("/home/u/.mcpp/bmi/deadbeef0123abcd/deps/mcpplibs/mcpplibs.cmdline@0.0.1");
+    EXPECT_EQ(k.dir(), expected);
     EXPECT_EQ(k.manifestFile().filename().string(), "manifest.txt");
     EXPECT_EQ(k.bmiDir().filename().string(),       "gcm.cache");
     EXPECT_EQ(k.objDir().filename().string(),       "obj");

tests/unit/test_manifest.cpp

@@ -398,7 +398,7 @@ kind = "lib"
     EXPECT_TRUE(m->lib.path.empty());
     EXPECT_TRUE(mcpp::manifest::has_lib_target(*m));
     auto root = mcpp::manifest::resolve_lib_root_path(*m);
-    EXPECT_EQ(root.string(), "src/tinyhttps.cppm");
+    EXPECT_EQ(root, std::filesystem::path("src/tinyhttps.cppm"));
 }
 
 TEST(Manifest, LibRootBareNameNoNamespace) {
@@ -412,7 +412,7 @@ kind = "lib"
     auto m = mcpp::manifest::parse_string(src);
     ASSERT_TRUE(m.has_value()) << m.error().format();
     auto root = mcpp::manifest::resolve_lib_root_path(*m);
-    EXPECT_EQ(root.string(), "src/gtest.cppm");
+    EXPECT_EQ(root, std::filesystem::path("src/gtest.cppm"));
 }
 
 TEST(Manifest, LibRootExplicitOverride) {