[AI] Refactor Test Coverage - Centralized MockAgent

[KCarretto]

This PR centralizes scattered MockAgent test implementations found across the eldritch standard libraries into a single unified eldritch-mockagent crate inside the testutils directory.

By unifying this codebase, duplicated boilerplate testing code is eliminated, making it easier to extend eldritch_agent::Agent behavior mocks in the future.

Key Changes

• Created implants/lib/eldritch/testutils/eldritch-mockagent.
• Linked eldritch-mockagent to Cargo.toml as a dev-dependency for eldritch-libagent, eldritch-libassets, eldritch-libpivot, and eldritch.
• Refactored all affected tests to utilize eldritch_mockagent::MockAgent instead of local structs.
• Confirmed stability with cargo check and cargo test passing smoothly.

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PR created automatically by Jules for task 13145434703601781316 started by @KCarretto

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[github-actions]

Summary

Tests 📝	Passed ✅	Failed ❌	Skipped ⏭️	Other ❓	Flaky 🍂	Duration ⏱️
2820    ±0	2820    ±0	0    ±0	0    ±0	0    ±0	0    ±0	1ms    ±0

Previous Results

Build 🏗️	Result 🧪	Tests 📝	Passed ✅	Failed ❌	Skipped ⏭️	Other ❓	Flaky 🍂	Duration ⏱️
#1736	✅	2820	2820	0	0	0	0	36.1s

Insights

Average Tests per Run	Total Flaky Tests	Total Failed	Slowest Test (p95)
2820	0	0	5.9s

Slowest Tests

Test 📝	Results 📊	Duration (avg) ⏱️	Duration (p95) ⏱️
TestDockerExecutor_Build_ContextCancellation	1	5.9s	5.9s
eldritch-libsys: std::dll_inject_impl::tests::test_dll_inject_simple	1	5.2s	5.2s
TestInteractiveShell	1	5.1s	5.1s
TestOtherStreamOutput	1	5.0s	5.0s
imix::bin/imix: install::tests::test_install_execution	3	1.8s	5.0s
imix::bin/imix: install::tests::test_install_execution	3	1.8s	5.0s
imix::bin/imix: install::tests::test_install_execution	3	1.8s	5.0s
TestDockerExecutor_Build_SimpleEcho	1	3.9s	3.9s
imix::bin/imix: tests::task_tests::test_task_streaming_error	3	3.0s	3.0s
imix::bin/imix: tests::task_tests::test_task_streaming_error	3	3.0s	3.0s

_{🎉 No failed tests in this run. | 🍂 No flaky tests in this run.}

Github Test Reporter by CTRF 💚