fix: max filepath length on windows (#16552)

# Description

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Windows traditionally limits many file operations to `MAX_PATH` (260
characters). Deeply nested plugin packages can exceed this limit during
`.whl` extraction, leaving files missing and causing the plugin to fail
to load.

This change adds a shared extended_path helper that prepares paths for
Windows file operations using the extended-length prefixes `\\?\` or
`\\?\UNC\`. The helper is used for ZIP archive I/O and extraction
destinations, including plugin wheel extraction. This avoids relying on
the Windows long-path setting, which changes machine-wide settings.

Paths remain unprefixed outside file operations. Code that bypasses the
shared ZIP helpers may still require separate long-path handling.

See [Microsoft's documentation on path length
limitation](https://learn.microsoft.com/en-us/windows/win32/fileio/maximum-file-path-limitation?tabs=registry)

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## Tests

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changes made in this PR.
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Tested on Windows 11 by using a portable installation of OrcaSlicer and
placing it in some really long filepath length e.g.
`C:/somename/<240 characters long folder path>/OrcaSlicer` and then
running and trying to install any plugin locally or on OrcaCloud.

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tests/libslic3r/test_utils.cpp

@@ -521,3 +521,49 @@ TEST_CASE("ascii_iequals compares ASCII letters regardless of case", "[Utils]")
     CHECK_FALSE(ascii_iequals("[", "{"));
     CHECK_FALSE(ascii_iequals("@", "`"));
 }
+
+TEST_CASE("extended_path turns a Windows path into its long-path form", "[Utils]") {
+#ifdef _WIN32
+    namespace fs = boost::filesystem;
+
+    SECTION("a normal absolute drive path is prefixed") {
+        CHECK(extended_path(fs::path(R"(C:\models\model.3mf)")).wstring() == LR"(\\?\C:\models\model.3mf)");
+    }
+    SECTION("separators are made native") {
+        CHECK(extended_path(fs::path("C:/models/model.3mf")).wstring() == LR"(\\?\C:\models\model.3mf)");
+    }
+    SECTION("dot segments are collapsed before prefixing") {
+        // The "\\?\" prefix disables Win32 normalisation, so "." and ".." must be gone beforehand.
+        CHECK(extended_path(fs::path(R"(C:\models\..\model.3mf)")).wstring() == LR"(\\?\C:\model.3mf)");
+    }
+    SECTION("a trailing separator is dropped, not turned into a dot element") {
+        CHECK(extended_path(fs::path(R"(C:\models\)")).wstring() == LR"(\\?\C:\models)");
+    }
+    SECTION("a UNC path becomes an extended UNC path") {
+        CHECK(extended_path(fs::path(R"(\\server\share\model.3mf)")).wstring() == LR"(\\?\UNC\server\share\model.3mf)");
+    }
+    SECTION("an already extended path is returned unchanged") {
+        const fs::path extended(R"(\\?\C:\models\model.3mf)");
+        CHECK(extended_path(extended) == extended);
+    }
+    SECTION("a device path is returned unchanged") {
+        const fs::path device(R"(\\.\C:\models\model.3mf)");
+        CHECK(extended_path(device) == device);
+    }
+    SECTION("a bare device path without a root directory is returned unchanged") {
+        // Not "absolute" by Boost's rules, so it must be recognized before absolutizing.
+        const fs::path device(R"(\\.\PhysicalDrive0)");
+        CHECK(extended_path(device) == device);
+    }
+    SECTION("a relative path is completed against the working directory") {
+        const fs::path result = extended_path(fs::path("model.3mf"));
+        CHECK(result.wstring().rfind(L"\\\\?\\", 0) == 0);
+        CHECK(result.filename() == fs::path("model.3mf"));
+    }
+#else
+    SECTION("non-Windows returns the path unchanged") {
+        const boost::filesystem::path p = boost::filesystem::temp_directory_path() / "model.3mf";
+        CHECK(extended_path(p) == p);
+    }
+#endif
+}