test: add failing tests for cost extraction wrong index bug (#555)

Add unit and E2E tests that detect incorrect cost/model extraction
in sync_orchestration.py. The sync loop reads result[1] as cost for
all operations, but generate returns cost at [2], and crash/fix/verify
return cost at [4]. Tests verify 13 failure cases and 3 regression guards.

Unit tests: test_e2e_issue_555_cost_extraction_wrong_index.py (16 tests)
E2E tests: test_e2e_issue_555_sync_cost_extraction.py (13 tests)

Fixes #555

Author: Serhan-Asad