Add storage-layout snapshot test enforcing stable persistent/instance/temporary key namespaces

[Baskarayelu]

Description

A silent rename of a storage key in src/storage.rs would orphan all existing data on a deployed contract. Add a snapshot test that serializes every storage-key constructor (InvoiceStorage::invoices_by_business, BidStorage::bids_by_invoice, etc.) for a fixed canonical input set and asserts the resulting key bytes against a committed snapshot. Any key drift becomes a deliberate, reviewable change.

Requirements and context

• Secure: snapshot deletions require admin review; renames force a migration plan.
• Tested: snapshot covers every public key-builder in src/storage.rs.
• Documented: docs/storage-key-stability.md.
• Reference: src/storage.rs.

Suggested execution

git checkout -b feature/storage-key-snapshot

• Add src/test_storage_key_layout.rs enumerating key builders.
• Persist snapshot under src/test_snapshots/storage_keys.txt.
• Docs: docs/storage-key-stability.md describing migration policy.
• Rust doc /// comments on the key builders noting "BREAKING: rename requires migration".
• Validate that persistent vs instance vs temporary storage classes are tagged.

Test and commit

Run cargo test test_storage_key_layout. Cover edge cases for every storage class. Include security note about data orphaning risk.

Example commit message

test(storage): add storage-key layout snapshot to prevent silent migrations

Guidelines

• Minimum 95% test coverage
• Clear documentation in docs/storage-key-stability.md
• Timeframe: 96 hours