Ledger JSON data now lives next to the code that owns its path
convention (mapping_validator.ledger_path_for) instead of a separate
top-level core/ directory.
Relocates the ledger audit/report logic under strategies/unit_tests to
match the harness's strategy-scoped layout. Now composes the schema
from shared.parity.ledger and the enumerators from python_runner.py/
rust_runner.py instead of owning that logic inline.
python_runner.py owns walking a Python test file's AST for test_*
functions and classes, separated out ahead of the strategies/unit_tests
mapping_validator restructure.
