Implement chunked file reporting in Eldritch

[KCarretto]

Implement file chunking for report.file in Eldritch to prevent memory issues with large files.

• Updated Agent trait in eldritch-agent to support streaming via Iterator.
• Implemented FileChunkIterator in eldritch-libreport with 1MB chunk size.
• Updated ImixAgent to stream chunks to transport using a background thread.
• Updated mocks and fake implementations in eldritch-libagent, eldritch-libassets, eldritch-libpivot, and tests.
• Added integration test test_report_large_file_via_eldritch in imix to verify 100MB file upload behavior.

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PR created automatically by Jules for task 14733173212644407774 started by @KCarretto

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[github-actions]

Summary

Tests 📝	Passed ✅	Failed ❌	Skipped ⏭️	Other ❓	Flaky 🍂	Duration ⏱️
2564    ±0	2564    ±0	0    ±0	0    ±0	0    ±0	0    ±0	1ms    ±0

Previous Results

Build 🏗️	Result 🧪	Tests 📝	Passed ✅	Failed ❌	Skipped ⏭️	Other ❓	Flaky 🍂	Duration ⏱️
#929	✅	2564	2564	0	0	0	0	29.6s

Insights

Average Tests per Run	Total Flaky Tests	Total Failed	Slowest Test (p95)
2564	0	0	5.2s

Slowest Tests

Test 📝	Results 📊	Duration (avg) ⏱️	Duration (p95) ⏱️
eldritch-libsys: std::dll_inject_impl::tests::test_dll_inject_simple	1	5.2s	5.2s
imix::bin/imix: install::tests::test_install_execution	3	1.2s	3.4s
imix::bin/imix: install::tests::test_install_execution	3	1.2s	3.4s
imix::bin/imix: install::tests::test_install_execution	3	1.2s	3.4s
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
imix::bin/imix: tests::task_tests::test_task_streaming_error	3	3.0s	3.0s
imix::bin/imix: tests::task_tests::test_task_streaming_output	3	3.0s	3.0s
imix::bin/imix: tests::task_tests::test_task_streaming_output	3	3.0s	3.0s
imix::bin/imix: tests::task_tests::test_task_streaming_output	3	3.0s	3.0s

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

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