🏁 Fix dynamic loading of QDMI device DLLs on Windows when an absolute path is provided (#1720)

## Description

This fixes an oversight in #1694 that broke dynamic QDMI library loading
on Windows and was discovered in
iqm-finland/QDMI-on-IQM#63
If an absolute path is provided, the implementation now falls back to
the previously-working one that used the simpler `LoadLibraryW` for
loading the DLL.

I'll to a test run of this PR in the QDMI-on-IQM repo before we merge
and release.

AI (Claude Code) was used to diagnose the issue and come up with
potential solutions.
The actual solution was implemented manually.

## Checklist

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- [x] The pull request only contains commits that are focused and
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new warnings.
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- [x] I have reviewed my own code changes.

**If PR contains AI-assisted content:**

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Signed-off-by: Lukas Burgholzer <burgholzer@me.com>

Author: burgholzer

CHANGELOG.md

@@ -25,6 +25,10 @@ This project adheres to [Semantic Versioning], with the exception that minor rel
 - ⬆️ Require LLVM 22.1 for C++ library builds ([#1549]) ([**@burgholzer**], [**@denialhaag**])
 - 📦 Build MLIR by default for C++ library builds ([#1356]) ([**@burgholzer**], [**@denialhaag**])
 
+### Fixed
+
+- 🏁 Fix dynamic loading of QDMI device DLLs on Windows when an absolute path is provided ([#1720]) ([**@burgholzer**])
+
 ### Removed
 
 - 🔥 Remove the density matrix support from the MQT Core DD package ([#1466]) ([**@burgholzer**])
@@ -389,6 +393,7 @@ _📚 Refer to the [GitHub Release Notes](https://github.com/munich-quantum-tool
 
 <!-- PR links -->
 
+[#1720]: https://github.com/munich-quantum-toolkit/core/pull/1720
 [#1719]: https://github.com/munich-quantum-toolkit/core/pull/1719
 [#1709]: https://github.com/munich-quantum-toolkit/core/pull/1709
 [#1702]: https://github.com/munich-quantum-toolkit/core/pull/1702

src/qdmi/driver/Driver.cpp

@@ -74,10 +74,14 @@ namespace {
 [[nodiscard]] auto loadDeviceLibrary(const std::string& libName) -> HMODULE {
   const auto requested = std::filesystem::path(libName);
 
-  const std::filesystem::path path = requested.has_parent_path()
-                                         ? requested
-                                         : getDriverDirectory() / requested;
+  if (requested.has_parent_path()) {
+    // A directory component was supplied: Directly load the library.
+    return LoadLibraryW(requested.wstring().c_str());
+  }
 
+  // Bare filename: resolve relative to the driver's own directory so that
+  // builtin device DLLs installed next to the driver are found reliably.
+  const auto path = getDriverDirectory() / requested;
   return LoadLibraryExW(path.wstring().c_str(), nullptr,
                         LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR |
                             LOAD_LIBRARY_SEARCH_DEFAULT_DIRS);