Accounts Refactor PR 1: Adding account -> [credential_id] mapping

[citizen-stig]

Description

PR 1 of the accounts refactor series. Introduces a new account_owners authorization set alongside the existing accounts map and stops writing to the legacy map from every code path. The legacy map remains readable so pre-upgrade state keeps routing.

What changed

• New state: account_owners: StateMap<(address, credential_id), bool>.
• InsertCredentialId now writes account_owners, not accounts.
• Genesis writes authorizations to account_owners.
• resolve_sender_address becomes read-only (no auto-create on miss).
• New capabilities: is_authorized(addr, cred) and is_authorized_for(addr, cred).
• accounts map kept purely as a read-only legacy fallback. No new writers.
• hyperlane-solana-register migrated from resolve_sender_address to is_authorized_for.
• Map uses boolean instead of unit type () because of limitations of rockbound: Refactoring for more explicit sentinel values handling rockbound#50

Trade-offs / behavioral deltas

• InsertCredentialId(X) from sender A no longer makes X route to A. It only authorizes X for A in account_owners. When X later signs a V0 tx, the resolver returns X.into() (stateless default), unless a pre-upgrade entry exists in legacy accounts. Fund the canonical address (or rely on a pre-upgrade entry) if you need X to draw gas from A.
• The "no hijacking" guard is narrower. exit_if_credential_exists now checks (sender, credential) in account_owners instead of global credential uniqueness in accounts. Authorizing someone else's credential for your own address now succeeds — harmless, since they still need the private key to sign.
• get_account(credential_id) returns AccountEmpty for post-PR credentials. New writes don't land in accounts. A get_addresses_for_credential query for the new model ships in a follow-up; tooling owners should plan accordingly.
• is_authorized_for gives legacy mappings exclusive priority. If a credential has a legacy accounts entry, only that address is authorized (canonical match and account_owners are not consulted). Doc updated to reflect this; code relies on the invariant that no code path writes both maps for the same credential.

Backward compatibility

• On-chain state: pre-upgrade accounts entries keep routing until explicitly migrated.
• Wire: AccountConfig, CallMessage, and tx schema unchanged.
• Client-visible regression: get_account (see above).

Known gaps / deferred

• DrainLegacyAccounts migration and get_addresses_for_credential query land in a later PR.
• resolve_sender_address is now pure-read but still takes &mut self and StateAccessor, duplicating resolve_sender_address_read_only. Two callers in sov-capabilities need migration before the mutable variant can be deleted — deferred.
• is_authorized_for legacy-first precedence is not enforced in code; relies on "no writer touches both maps for the same credential". Fine today, brittle if a future migration ever violates it.

---

• Will be done when merging to dev I have updated CHANGELOG.md with a new entry if my PR makes any breaking changes or fixes a bug. If my PR removes a feature or changes its behavior, I provide help for users on how to migrate to the new behavior.
• I have carefully reviewed all my Cargo.toml changes before opening the PRs. (Are all new dependencies necessary? Is any module dependency leaked into the full-node (hint: it shouldn't)?)

Linked Issues

• Related to sov-accounts refactoring and extending #2772

Testing

New tests added in sov-accounts integration tests (test_setup_multisig_and_act, test_resolve_address_with_multi_credential_ownership, etc.). Existing test_multisig_signature_verification in auth_eip712 updated to seed the multisig's canonical address at genesis under the new model.

Docs

sov-accounts/README.md expanded with the three-relation model (legacy mapping / stateless canonical / explicit authorization). Function docstrings updated.