Add DPI-aware wrapper methods for Win32 system metrics and window sizing

[Copilot]

Adds convenient type-safe wrappers for Win32 DPI APIs to simplify DPI-aware window management and system metric retrieval.

Changes

• New DpiApi class with 6 wrapper methods:

  • GetSystemMetrics() / GetSystemMetricsForWindow() - DPI-scaled system metrics
  • AdjustWindowRect() / AdjustWindowRectForWindow() - DPI-aware window rect calculation from client rect
  • GetSystemParametersInfo<T>() / GetSystemParametersInfoForWindow<T>() - Type-safe system parameters with DPI

• P/Invoke declarations added to NativeDpiMethods:

  • GetSystemMetricsForDpi()
  • AdjustWindowRectExForDpi()

• Tests for all new wrapper methods

Usage

// Get DPI-scaled metrics
var borderWidth = DpiApi.GetSystemMetrics(SystemMetric.SM_CXBORDER, dpi: 144);
var screenWidth = DpiApi.GetSystemMetricsForWindow(SystemMetric.SM_CXSCREEN, hwnd);

// Calculate window rect from client rect with DPI awareness
var clientRect = new NativeRect(0, 0, 800, 600);
var windowRect = DpiApi.AdjustWindowRect(
    clientRect, 
    WindowStyleFlags.WS_OVERLAPPEDWINDOW,
    dpi: 144);

// Type-safe system parameters
var iconMetrics = DpiApi.GetSystemParametersInfo<IconMetrics>(
    SystemParametersInfoActions.SPI_GETICONMETRICS, 
    dpi: 192);

All methods return nullable types for clean error handling and support both explicit DPI values and window handle-based DPI detection.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Add more Win32 DPI calls</issue_title>
<issue_description>Extend the functionality in Dapplo.Windows.Dpi a more convenient way to call:

• https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-getsystemmetricsfordpi
• https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-systemparametersinfofordpi
• https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-adjustwindowrectexfordpi

So not just the pinvoke with the metrics which returns result.
Place these in DpiApi.cs

Hint: The Enum for the metrics is already available as Dapplo.Windows.User32.Enums.SystemMetric but some metrics have specific results which are also an enum.

Consider other Windows DPI relevant things...
</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Add more Win32 DPI calls #18

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}