Add Flight retrieval: flights (GetFlightInfo) and get (DoGet)

[T20354]

Summary

Adds the retrieval side of Arrow Flight, complementing the existing put (DoPut) and action (DoAction) operations.

• client.flights({ path } | { cmd }) — GetFlightInfo. Resolves to a FlightInfoResult with raw() (the underlying FlightInfo) and endpoints().
• client.get(ticket) — DoGet. Resolves to a FlightResult with table(), rows(), and raw(); the stream is drained once and the derived views are memoized.
• new FlightClient(location, …) — now accepts a host:port, a grpc:// / grpc+tls:// URI, or a Flight Location object (parseLocation). Redeeming a remote endpoint is explicit: open a client for the endpoint's location, get, then close.

Internals

• src/ipc.ts now owns both directions of the FlightData⇄Arrow IPC framing. flightDataToTable reassembles a DoGet stream into a Table; put.ts imports parseIPCMessages back. Only the message header is padded to 8 bytes — the body is emitted verbatim, since the reader takes the body length from the IPC message's own bodyLength field, not from the framing.
• convert.ts adds tableToRows, which recurses into nested structs/lists to produce plain objects (64-bit ints surface as bigint, timestamps as Date).

Design notes

• Named flights rather than getFlightInfo; ListFlights is out of scope and would need a different name if added.
• Connection ownership is explicit — the library holds no pool. The constructor uses a deliberate allowlist (bare address + grpc[+tls]://); other schemes throw.
• Out of scope: ListFlights / GetSchema / PollFlightInfo, HTTP and grpc+unix locations, automatic multi-endpoint fan-out, and schema decoding.

Testing

npm run build && npm test — 63/63 pass. New coverage: the flights / get operations, the IPC round-trip (including non-8-aligned data_header, multi-record-batch streams, and nested structs/nulls), deep tableToRows, and parseLocation edge cases. An automated review pass was run; its findings — the undefined-ticket guard, body-padding safety, deep row conversion, and location edge cases — are incorporated.

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