Add testFetchPendingInvoicesAccepted to explicitly verify the state
filtering behaviour of FetchPendingInvoices across all four contract
states:
ContractOpen (state 0) – must be returned
ContractAccepted (state 3) – must be returned
ContractSettled (state 1) – must be excluded
ContractCanceled (state 2) – must be excluded
This directly exercises the `state IN (0, 3)` predicate introduced in
the FetchPendingInvoices SQL query and addresses the review request for
explicit test coverage of the new targeted query variants. The test
runs against the KV, SQLite, and Postgres backends.
ziggie
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