[AI] Expand Test Coverage - eldritch-core/lexer

[KCarretto]

This PR adds a new integration test file implants/lib/eldritch/eldritch-core/tests/lexer_more_edges.rs to the eldritch-core crate. The tests target specific edge cases in the Lexer that were previously under-tested or documented only implicitly.

Key coverage areas added:

• Integer Overflow: Verifies that integers exceeding i64::MAX are parsed as 0 (current unwrap_or(0) implementation).
• Mixed Indentation: verifies that the lexer counts characters for indentation regardless of type (tabs vs spaces).
• Token Separation: Confirms that sequences like + = are tokenized differently from +=.
• Keyword Lookalikes: Ensures that identifiers starting with keywords (e.g., defe) are correctly parsed as identifiers.
• Nested F-Strings: Tests the recursion limit and parsing of f-strings within f-strings.
• Unicode Escapes: Documents that \uXXXX sequences are currently treated as literal characters, not unicode escapes.
• Error Handling: verifies error tokens for unterminated strings at EOF.

These tests were run 20 times locally to ensure stability and passed successfully. Full crate tests were also run to ensure no regressions.

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PR created automatically by Jules for task 1041214475409502697 started by @KCarretto

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[github-actions]

Summary

Tests 📝	Passed ✅	Failed ❌	Skipped ⏭️	Other ❓	Flaky 🍂	Duration ⏱️
2565    ±0	2565    ±0	0    ±0	0    ±0	0    ±0	0    ±0	1ms    ±0

Previous Results

Build 🏗️	Result 🧪	Tests 📝	Passed ✅	Failed ❌	Skipped ⏭️	Other ❓	Flaky 🍂	Duration ⏱️
#828	✅	2565	2565	0	0	0	0	16.9s

Insights

Average Tests per Run	Total Flaky Tests	Total Failed	Slowest Test (p95)
2565	0	0	5.1s

Slowest Tests

Test 📝	Results 📊	Duration (avg) ⏱️	Duration (p95) ⏱️
eldritch-libsys: std::dll_inject_impl::tests::test_dll_inject_simple	1	5.1s	5.1s
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_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
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

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

Github Test Reporter by CTRF 💚

🔄 This comment has been updated