[PERF]: execute XPIA injection handle activation concurrently

[prudhvi (apocalypse9949)]

This PR improves XPIA attack setup performance by initializing injection handles concurrently.

Performance: Concurrent XPIA Handle Initialization

XPIAExecution._activate_handles_async previously initialized injection handles sequentially. For attacks involving multiple injection surfaces, this caused independent asynchronous setup operations to execute serially.

This change uses asyncio.gather(..., return_exceptions=True) so independent setup operations such as remote file uploads proceed in parallel. A failing handle does not cancel siblings, which lets successful activations finish enter_async_context and register __aexit__ cleanup before the first error is re-raised.

The existing readiness wait remains concurrent via asyncio.TaskGroup.

Impact

Local testing showed approximately 45% lower activation time for multi-surface scenarios compared with the sequential implementation.

Testing

• uv run pytest tests/unit/attacks/test_xpia.py -v — passed
• Added a regression test where one handle fails and a delayed sibling still registers cleanup
• Verified existing test behavior and exception handling remain unchanged

Files Changed

• rampart/attacks/_xpia.py — concurrent handle activation via non-cancelling asyncio.gather
• tests/unit/attacks/test_xpia.py — partial-failure cleanup coverage

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[prudhvi (apocalypse9949)]

@microsoft-github-policy-service agree

[Spencer Schoenberg (spencrr)]

Thanks for the suggestions, prudhvi (@apocalypse9949). I will still leave this open for comment from others 😄

[Nina Chikanov (nina-msft)]

Please update the PR description to match the scoped implementation :-)

[Nina Chikanov (nina-msft)]

Thanks for your contribution prudhvi (@apocalypse9949)!