Add result JSON contract test

[yoshifuminakamura]

Summary

• add a focused shell test for the common Result JSON emitter in scripts/result.sh
• cover source_info, input_info, FOM breakdown, pipeline timing, execution trigger, environment snapshot, and build cache metadata
• run the new contract test in the existing Result Server Tests profile-data-shell job

Testing

• bash scripts/tests/test_result_common_json_contract.sh
• shellcheck -S error scripts/tests/test_result_common_json_contract.sh
• bash scripts/tests/test_process_and_send_results.sh
• bash scripts/tests/test_estimation_common_json_contract.sh
• .venv/bin/python result_server/tests/run_result_server_tests.py
• profile-data-shell local suite
• git diff --check
• python3 scripts/tests/check_text_integrity.py
• python3 scripts/tests/check_commit_messages.py