refactor(core)!: remove Source, pump_sink, Connector and TopicProvider (design 054)

[lxsaah]

Stage 16 of the design 054 implementation plan: remove the old connector SPI. Breaking.

Base: feat/054-connector-boundary. This PR first targeted main so CI would run the full matrix; that run passed on every check (Format and Lint, Build & Test, Embedded Cross-compilation, Comprehensive Development Check, Build Documentation, Bench Gate, Miri, WASM). To make that possible, main was merged in: it brings #284 (Maximum Packet Size in the embedded CONNECT) into the feature branch. Its conflicts keep the branch's side, which already sends the same CONNECT properties.

Removed

• aimdb-core:
  • Source, pump_source, pump_sink (session/pump.rs)
  • the Connector trait (ConnectorConfig and PublishError stay)
  • SerializedReader, SerializedSource, SerializedValue, SerializedValueInto, SerializedPayload, RecvSerializedFuture, RecvSerializedIntoFuture
  • SourceFactoryFn, TopicProvider, with_topic_provider
  • OutboundRoute, AimDb::collect_outbound_routes
• Now crate-private: Router and AimDb::inbound_router; InboundDispatch uses them. ConnectorLink carries only the route factory.
• Embassy adapter: EmbassySinkRaw, EmbassySink, EmbassySourceRaw, EmbassySource. connectors.rs keeps into_box_future and NetStack.
• KNX:
  • embassy-sync and the optional critical-section dependency are dropped.
  • critical-section-std-impl is kept as a deprecated no-op, following the crate's existing pattern for deprecated features. It is removed from the README, the Tokio demo and codegen output.

Migrated tests

• Core:
  • The fused_reader_* cases now run against OutboundRoutes through a scripted buffer.
  • The inbound_router_* tests are folded into the inbound_dispatch_* ones.
  • pump_source_routes_through_the_given_router is removed.
• Other crates:
  • aimdb-data-contracts link_codec.rs and MQTT link_ext_tests.rs now use OutboundRoutes::routes()/next and InboundDispatch.
  • In the Tokio adapter's outbound_routes.rs, the provider-rejection test is removed and the route-info test no longer compares against collect_outbound_routes.
  • The KNX test for with_topic_provider rejection is removed.

Bench

The inbound_route*, inbound_pump_source_minimal, outbound_scratch_* and outbound_owned_static_topic rows are removed and the baseline replaced. Every remaining row matches the design's §5 targets:

Row	Allocations per message
inbound_dispatch, inbound_dispatch_pattern, inbound_dispatch_keyed_known	0
inbound_dispatch_keyed_new	1
outbound_next_static_topic, outbound_next_written_topic	0
outbound_next_owned	1
outbound_next_round_robin, outbound_next_parked	0

Verified locally

• Test legs:
  • all core Makefile test legs
  • aimdb-data-contracts legs
  • MQTT std
  • aimdb-tokio-adapter
  • KNX std
• Gate: make bench-gate passes.
• Leftover names: a grep for the removed names finds them only in CHANGELOGs, design docs and release notes.
• make check: stopped once in clippy with a build-directory error (failed to create encoded metadata). That's a devcontainer filesystem problem, not a lint: rerunning the failed leg (aimdb-websocket-connector) was clean. CI is the full run.

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