fix(alita): preserve generated tool results with stdout logs

[bitkira]

Summary

• add a unique result marker for Alita generated tools so user stdout logs do not break result parsing
• preserve stdout/stderr logs separately while returning the structured generated tool result
• keep legacy full-JSON output compatibility and avoid guessing JSON from unmarked mixed output
• add regression coverage for noisy stdout, post-result output, marker collisions, legacy JSON output, and the real Python executor

Closes #255

Tests

• .venv/bin/python -m pytest tests/src/tools/test_alita_generated_code_tool.py -q
• .venv/bin/python -m pytest tests/src/tools/test_alita_generated_code_tool.py tests/src/core/test_dependency_extras.py -q
• .venv/bin/python -m ruff check evoagentx/tools/alita_agent.py tests/src/tools/test_alita_generated_code_tool.py
• git diff --check