Drop the embassy-sync git patch once a release carries poll_next_message / poll_changed #386

Tracking issue for moving embassy-sync (and the two crates that follow it) back to crates.io releases.

Background

aimdb-embassy-adapter/src/buffer.rs polls Subscriber::poll_next_message and Receiver::poll_changed directly. Both are merged upstream but not in embassy-sync 0.8.0, still the latest on crates.io. The workspace therefore patches them in (Cargo.toml, [patch.crates-io], added in #343 for #341):

• embassy-sync → embassy git rev 03c826f
• embassy-net-driver-channel and embassy-net-driver → same rev. Published embassy-net-driver-channel 0.4.0 calls the pre-guard zerocopy_channel API the patched embassy-sync no longer has, and its driver trait must be the same instance embassy-net sees.

Consequences while the patch is in place:

• Publishing: patches are not published, so the packaged aimdb-embassy-adapter cannot build its embassy-sync feature for a downstream user. The Makefile publishes it without verification (PUBLISH_NO_VERIFY) for this reason. The vendored copy carries the same 0.8.0 version as the registry release, so nothing flags the mismatch.
• Other embassy bumps: pinning further embassy-* crates to git is constrained by this rev. E.g. pointing embassy-stm32 at 03c826f to pick up the BufferedUart TX fix fails to resolve (embassy-time-driver conflict), see Serial demo client hangs against the NUCLEO-H563ZI until the board is rebooted once #382 / Drop the EmbassyUart flush-per-write workaround once embassy-stm32 ships the BufferedUart TX fix #385.

To do once a release carries both APIs

• Bump embassy-sync in the workspace Cargo.toml and in aimdb-mqtt-connector/Cargo.toml (it declares its own embassy-sync = "0.8.0").
• Remove the three [patch.crates-io] entries and their comment; bump embassy-net-driver-channel / embassy-net-driver (or embassy-net) to releases that match the new embassy-sync.
• Drop aimdb-embassy-adapter from PUBLISH_NO_VERIFY in the Makefile and update its comment (it still points at make publish is broken: three connectors are unpublished and a dev-dependency cycle blocks any ordering #242).
• Update the comments that point at the patch (aimdb-mqtt-connector/Cargo.toml, aimdb-embassy-adapter/src/buffer.rs around the poll_* calls).
• Check whether this unblocks Drop the EmbassyUart flush-per-write workaround once embassy-stm32 ships the BufferedUart TX fix #385 (embassy-stm32 with the BufferedUart fix) so both can move together.
• Build the embedded targets (make test-embedded or equivalent) and smoke-test one Embassy demo on the NUCLEO-H563ZI.