feat: add configuration getters to RefundVault and ReceiptAnchor (#195)

[aurorabini]

Configuration Getters

Adds read-only getters for all stored configuration values that were previously
only accessible via raw ledger entry reads.

RefundVault

• get_admin() → merchant address
• get_token() → payment token address
• get_refund_window() → refund window in ledgers
• is_paused() → whether the vault is paused

ReceiptAnchor

• get_admin() → merchant address
• get_pruned_up_to() → pruned-up-to batch ID

All return NotInitialized (rather than trapping) when called on an
uninitialized contract, matching the pattern established in #153.

Closes #195

[mergekeeper]

Needs changes

The PR implements the requested configuration getters for both contracts and uses proper error handling, but it is missing the required tests and the persistent-storage audit specified by linked issue #153.

• contracts/refund-vault/src/lib.rs:760: Missing unit or integration tests verifying that getters read back each value correctly after initialize and setters, and return NotInitialized when uninitialized (Issue Instance storage reads use unwrap() and trap instead of returning typed errors #153/Config values are unreadable on-chain: no getter exposes the token, window, admin or pause state #195 requirements).

Reviewed commit: a71f5a2c7d21e6537dbe1ee68409710def292698.

[mergekeeper]

Needs changes

The PR implements the configuration getters requested in #195, but omits the changes for #153 (replacing unwrap() calls on instance storage reads across the contracts and adding a partial-state test or reporting the persistent storage audit).

• contracts/refund-vault/src/lib.rs: Issue #153 requires replacing all instance storage read unwrap() calls with ok_or(Error::NotInitialized)? across the codebase, which has not been fully addressed in this PR alongside issue #195.

Reviewed commit: 5ee408f33219e278c2ef1dd90c5be492a48488ae.

[mergekeeper]

Needs changes

The PR implements the requested configuration getters for both contracts and uses proper error handling, but it is missing the required tests and the persistent-storage audit specified by linked issue #153.

• contracts/refund-vault/src/lib.rs:760: Missing unit or integration tests verifying that getters read back each value correctly after initialize and setters, and return NotInitialized when uninitialized (Issue #153/#195 requirements).

Reviewed commit: a71f5a2c7d21e6537dbe1ee68409710def292698.