Add single WBC preinlet pipeflow example and WBC support to pipeflow_with_preinlet

[Umair747]

Motivation

• Provide an easy-to-run single-pass white blood cell (WBC) example for pipe flow with the preinlet boundary condition.
• Enable injecting WBCs via the existing preinlet infrastructure and expose WBC inputs for the pipeflow_with_preinlet case.

Description

• Add WBC handling to examples/pipeflow_with_preinlet/pipeflow_with_preinlet.cpp by including wbcHighOrderModel.h, registering the WBC cell type, setting minimum distance and outputs, and reporting WBC counts.
• Add WBC parameter and position files examples/pipeflow_with_preinlet/WBC.xml and WBC.pos.
• Add a new example examples/pipeflow_with_preinlet_single_wbc (source, CMakeLists.txt, config.xml, WBC.xml, WBC.pos, README, helper scripts and STL assets) and register it in examples/CMakeLists.txt.

Testing

• No automated tests were executed as part of this change.
• The new example was registered in examples/CMakeLists.txt so it can be built with cmake --build . --target "pipeflow_with_preinlet_single_wbc" (manual build/run expected by users).

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Codex Task