Add DEPTHAI_INSTALL_PREFIX to depthaiConfig.cmake, install libusb DLL for every depthai example

[lnotspotl]

The purpose of this PR is to introduce a new depthai-specific cmake constant called DEPTHAI_INSTALL_PREFIX to facilitate dependency installation for projects linking against depthai, especially those on Windows. This is paramount for users who build depthai with BUILD_SHARED_LIBS turned ON as the folder containing generated .dll libraries either has to be added to PATH or libraries contained within have to be copied over to the very location of a dependent executable.

The depthai-core-example makes use of this new variable, a PR for that project is opened here.

Additionally, this PR fixes ALL examples built on Windows when depthai-core is built as a shared library.

[Copilot]

Pull Request Overview

This PR introduces a new CMake variable DEPTHAI_INSTALL_PREFIX to help downstream projects locate depthai dependencies, particularly on Windows when building with shared libraries. It also ensures all depthai examples work correctly on Windows with shared libraries by automatically copying required DLLs.

• Adds DEPTHAI_INSTALL_PREFIX variable to the depthai CMake config for downstream dependency management
• Refactors the add_runtime_dependencies macro into a shared helper file for reusability
• Installs libusb runtime artifacts and copies DLLs for all examples to fix Windows shared library builds

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
cmake/depthaiConfig.cmake.in	Adds DEPTHAI_INSTALL_PREFIX variable calculation and version information
cmake/depthaiHelpers.cmake	New helper file containing the refactored add_runtime_dependencies macro
examples/cpp/CMakeLists.txt	Includes helper file and adds libusb DLL copying for all examples
CMakeLists.txt	Refactors macro to use helper file and adds libusb runtime artifact installation

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[Copilot]

The debug messages contain inconsistent terminology - some refer to 'core' while others use the actual target name. Line 23 should use '${depending_target}' instead of hardcoded 'core' for consistency.

[Serafadam]

I think we also need to do that for dynamic calibration library? I also think this makes add_runtime_dependencies obsolete (at least that was the case when building deb packages for ROS)

[lnotspotl]

You're making a really good point here. The issue was that when I tried installing the project, libusb-1.0.so would not be present as a runtime dependency but the dynamic_calibration library would. Turns out there was a bug in the add_runtime_dependencies macro that would override the required_dll_files variable every time it was invoked, thereby causing that only the last added runtime dependency would be added.

I guess this macro is still needed for libraries that we link against with PRIVATE visibility.

[moratom]

Test if the OpenCV is installed by choco and DepthAI core as a shared library, will it work? Can we make it work?

[lnotspotl]

Choco installs OpenCV without modifying the PATH env variable, so we do need to copy its dlls over for all our examples. With our current cmake setup, this happens automatically and examples work even when depthai-core is compiled as a shared library.