[Spicy-cream]

What problem does this PR solve?

URMA needs repeatable coverage for flow-control stalls, disconnects, resource exhaustion and mixed-size traffic across independent connections.

What is changed and the side effects?

• Add jetty-scoped mock faults for rejected posts, delayed credit/send completions and completion errors, with resource accounting.
• Add endpoint and RPC tests for backpressure, credit validation, pool exhaustion, resource recreation and disconnect recovery.
• Add three-mode CTest/CI coverage and a configurable connection-scale runner that checks response contents and connection IDs.
• Publish mock send completions after consuming source SGEs and keep mock resources alive while posting and polling.

Check List:

• URMA mock build and seven affected CTest targets pass.
• Ten fault and pool tests pass 100 consecutive iterations.
• 1,024 independent mock URMA connections pass 12 mixed-size rounds in event, polling and inline polling modes.
• URMA-disabled test compilation passes.