test: setattr/delattr hardening

[fracasula]

Description

Contract tests for this PR, which routes every sandbox write (obj.attr = v, del obj.attr, setattr(), delattr()) through a new write guard.

WARNING: The tests should pass once we have a new PYT release.

They live in integration_test/pytransformer_contract/security_hardening_contract_test.go and must merge together with the pytransformer PR.

What is pinned

The write guard defaults to shadow (record and allow), so both sides of the switch are covered across the container boundary:

• TestWriteGuardShadowContract — at the shipping default the write lands, the transformation runs to completion, transformer_write_guard_unsafe_total{kind} records it, and the alerted-on security series stays at zero.
• TestWriteGuardEnforceContract / TestWriteGuardDelattrContract — under SANDBOX_WRITE_GUARD_ENFORCE=true a write to a module, a foreign class, or a reserved name is refused and lands on transformer_security_violations_total.
• TestWriteGuardLibraryOwnershipContract — a transformation writing to its own library records nothing, the direction that decides whether the counter is readable at all.
• TestWriteGuardOwnershipRegistryContract — ownership is keyed by identity, so an unhashable class is not over-blocked and a forged __hash__/__eq__ cannot launder ownership.
• TestWriteGuardCounterUnitContract — the counter counts refused writes, not failed transformations.
• TestTestFlowSecurityMetricsContract / TestTestFlowEnforceContract — /test and /testRun replay their security signals onto the transformer_test_flow_* twins, never the production series.
• TestGetattrAndModuleGuardContract — the getattr value guard and the raw __getattribute__ / __getattr__ block.
• TestFactoryReprRiskContract — the new shadow-only telemetry: a transformation that both builds a factory-made class (namedtuple, three-argument type()) and renders text is flagged on transformer_factory_class_repr_risk_total, while a factory class that is never rendered stays quiet. It sizes the follow-up __module__ work and changes no behaviour.

The write-guard, preview-twin and factory-telemetry tests are candidate-only: the guard and those metrics are new, so no released baseline image exports them to compare against.

Linear Ticket

< Fixes PIPE-3322 >

Security

• The code changed/added as part of this pull request won't create any security issues with how the software is being used.

Test-only change. It locks the contract that the pytransformer sandbox blocks these escapes, that the write guard refuses non-user-owned writes under enforce while changing nothing at the shadow default, and that preview traffic never reaches the production security series.