[AI] Expand Test Coverage - eldritch-libagent

[KCarretto]

This PR drastically increases the test coverage for the eldritch-libagent module within the implants workspace.

It achieves this by:

1. Extending the MockAgent inside eldritch-mockagent to track and buffer RPC requests sent from the library.
2. Expanding implants/lib/eldritch/stdlib/eldritch-libagent/src/tests.rs with test_agent_library_methods to exercise all standard library methods available in the module (claim_tasks, fetch_asset, report_credential, report_file, report_process_list, report_task_output, etc).
3. Fixing a potential deadlock / race condition in report_file_impl.rs by dropping the tx sender immediately after dispatch to unblock receiver channels synchronously.

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PR created automatically by Jules for task 13749239737806643249 started by @KCarretto

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[github-actions]

Summary

Tests 📝	Passed ✅	Failed ❌	Skipped ⏭️	Other ❓	Flaky 🍂	Duration ⏱️
2947	2947	0	0	0	0	1ms

Previous Results

Build 🏗️	Result 🧪	Tests 📝	Passed ✅	Failed ❌	Skipped ⏭️	Other ❓	Flaky 🍂	Duration ⏱️
#1980	✅	2947	2947	0	0	0	0	43.4s

Insights

Average Tests per Run	Total Flaky Tests	Total Failed	Slowest Test (p95)
2947	0	0	6m 9s

Test Changes

0 test added, 0 removed

Slowest Tests

Test 📝	Results 📊	Duration (avg) ⏱️	Duration (p95) ⏱️
eldritch-libfile: std::list_recent_impl::tests::test_list_recent_default_args	3	4m 23s	6m 9s
eldritch-libfile: std::list_recent_impl::tests::test_list_recent_default_args	3	4m 23s	6m 9s
eldritch-libfile: std::list_recent_impl::tests::test_list_recent_default_args	3	4m 23s	6m 9s
TestDockerExecutor_Build_ContextCancellation	1	5.8s	5.8s
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
TestDockerExecutor_Build_SimpleEcho	1	3.2s	3.2s
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 💚