448 allow only 1 instance setting does nothing

[Hirogen]

This pull request introduces improvements to the "Allow Only One Instance" feature, focusing on better handling of file loading and active window tracking, as well as enhancing test coverage for IPC and window management logic. The changes ensure that when only one instance is allowed, files are loaded into the most recently activated window, and locked windows take priority. Several new unit tests have been added to verify these behaviors and document the intended logic.

Active Window Tracking and File Loading Improvements:

• The system now tracks the most recently activated log window using the new _mostRecentActiveWindow field in LogExpertProxy. When loading files with "Allow Only One Instance" enabled, files are loaded into this window, falling back to the most recently created window if no activation has occurred. [1] [2]
• The NotifyWindowActivated method is added to ILogExpertProxy and implemented in LogExpertProxy, allowing UI code to inform the proxy when a window is activated. This ensures correct window selection for file loading. [1] [2]
• The UI now calls NotifyWindowActivated in the OnLogTabWindowActivated event, enabling the new tracking mechanism.

"Allow Only One Instance" and Locked Window Logic:

• In NewWindowOrLockedWindow, if a locked window exists, it receives the files; otherwise, files are loaded in the most recent active window instead of always creating a new window. This fixes previous issues where new windows were created unnecessarily.

Testing Enhancements:

• New unit tests have been added for active window tracking, lock instance priority, and IPC message serialization. These tests verify correct window selection, fallback behavior, and message handling for the "Allow Only One Instance" feature. [1] [2]

Other Improvements and Maintenance:

• The obsolete ShowErrorMessageAllowOnlyOneInstances property in Preferences is now marked as [Obsolete] and ignored by JSON serializers, as it is no longer used or saved.
• Minor code cleanup and improved variable naming for clarity in the program entry point. [1] [2] [3]