v0.9.0

Breaking API redesign of the client and transaction surface.

• breaking: rename TxnContext -> Txn and NewTxnContext -> NewTxn
• breaking: InTxn now returns an exported, curated *ClientTxn (was the interface-typed Client): a transaction-scoped client that carries only record data-ops. Connection lifecycle (Close, WithRetry, schema and drop operations) and transaction entry (NewTxn, InTxn) are absent rather than hidden, so starting a transaction from within a transaction is unrepresentable at the type level. A package-level InTxn(tx *Txn) *ClientTxn is the sole constructor; Client.InTxn delegates to it
• feat: add ClientCore, the narrow record data-ops interface (Get, Insert, Upsert, Update, Delete, GetOrInsert, GetAndDelete, Query, QueryRaw) satisfied by both the connection Client and *ClientTxn; Client embeds it, and typed.Client[T], typed.Query[T], and typed.MultiQuery[T] bind to it so one typed client serves both the connection and transaction modes
• breaking: rename LoadOrStore -> GetOrInsert and LoadAndDelete -> GetAndDelete across the untyped and typed clients, with docs that lead with the operation, the single-winner concurrency contract, and the use cases (idempotent creation; single-use token consume); the cf. sync.Map lineage notes remain
• breaking: typed Client[T].Add -> Insert; typed clients gain QueryRaw and drop Iter (iterate via Query(ctx).IterNodes()) and NewTxnContext (transaction entry is a connection-client concern)
• breaking: delete the vestigial InsertRaw (identical to Insert since the unique-check unification) and the load-test RAW_INSERT mode built on it
• breaking: fold the generated-wrapper base into core as Entity[R] / AsEntity / Record(); UnwrapSchema -> AsRecord, probing Record(); the Schema marker interface -> Record (RecordTypeName)