feat(net): multi & managed for recvfrom & recvmsg

[Berrysoft]

Closes #833

Needs #832, #842, #843

This PR adds recv_from_multi, recv_msg_managed, and recv_msg_multi.

• recv_msg_managed requires a user-provided, not managed buffer for the cmsg.
• The multishot ops returns a custom result type to unify different platforms. It is a single buffer on io-uring, but multiple buffers on other platforms.

[Copilot]

Pull request overview

Adds managed and multishot receive APIs (including ancillary-aware variants) across compio-driver, compio-net, and compio-runtime, introducing unified result wrapper types to smooth over platform differences (io-uring single-buffer layout vs other backends).

Changes:

• Introduce driver-level ops/results for recv_from_multi, recv_msg_managed, and recv_msg_multi (poll/iour/iocp/stub + fusion wrappers).
• Extend runtime multishot stream handling to construct custom managed result items (RecvFromMultiResult, RecvMsgMultiResult).
• Add net-level public APIs + ancillary read traits for TCP/Unix streams, plus a new UDP recv_from_multi test.

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
compio-runtime/src/future/stream.rs	Generalize multishot managed stream item handling to support custom result wrappers.
compio-net/tests/buffer_pool.rs	Add coverage for new UDP multishot recv_from_multi.
compio-net/src/unix.rs	Implement ancillary managed/multi read traits for UnixStream using new recvmsg ops.
compio-net/src/udp.rs	Expose recv_from_multi, recv_msg_managed, and recv_msg_multi on UdpSocket.
compio-net/src/tcp.rs	Implement ancillary managed/multi read traits for TcpStream using new recvmsg ops.
compio-net/src/socket.rs	Wire socket-level managed/multi recv APIs to runtime submit/submit_multi.
compio-io/src/ancillary/io.rs	Add new ancillary read traits for managed buffers and multi streams.
compio-driver/src/sys/stub/op.rs	Add stub-backend OpCode impls for newly introduced managed/multi ops.
compio-driver/src/sys/poll/op.rs	Add polling-backend OpCode impls and refactor recv/send msg control storage.
compio-driver/src/sys/iour/op/mod.rs	Export new iour managed/multi recv ops and adjust recvfrom/sendto control handling.
compio-driver/src/sys/iour/op/managed.rs	Implement io-uring managed recvmsg + multishot recvmsg/recvfrom result parsing.
compio-driver/src/sys/iocp/op.rs	Add IOCP OpCode impls for new managed/multi ops.
compio-driver/src/sys/fusion/op.rs	Add fused ops + unified result wrapper types for cross-backend API consistency.
compio-driver/src/op/mod.rs	Re-export new managed/multi recv ops across cfgs.
compio-driver/src/op/managed.rs	Add non-io_uring managed/multi recv ops and result wrapper types.

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[George-Miao]

Let's split this into two PR's, one for driver and one for net

[Berrysoft]

OK. I'll split it.

[Copilot]

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

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