videre-sdk: name the one-poll driver for the seam it asserts

[mfw78]

What

Drop the rt module in videre-sdk and move its one-poll future driver into client.rs beside the VenueTransport seam, renamed from complete to poll_once returning Poll<F::Output>. Rewrite the doc to cite the real warrant: videre:venue/client@0.1.0 declares plain funcs, so a transport over the host import resolves on the first poll, and None/Pending means a foreign impl suspended, which the keeper macro folds to a fault. Update the emitted path in videre-macros/src/keeper.rs and every call site. Route the sweep.rs suspension arm through Retrier for parity with the ClientError::Venue arm.

Why

rt implied a scheduler where there is only a single poll, was the sole abbreviated module name, and collided with wit_bindgen::rt. complete asserted completion while the signature returned Option. The old doc over-claimed "guest host imports are synchronous", a warrant that does not hold for the whole runtime and prompted a rejected hoist into L1. After the M5 carve this becomes tag-pinned public API, so the naming must settle first.

Testing

cargo fmt --all -- --check; cargo clippy --workspace --all-targets --all-features --locked -D warnings; wasm32-wasip2 release build of all 16 modules plus the cow adapter (17 wasms); cargo nextest run --workspace --all-features --no-fail-fast --locked (795 passed); cargo test --doc --workspace --all-features --locked; RUSTDOCFLAGS="-D warnings" cargo doc --workspace --no-deps --locked; check-venue-agnostic.sh; check-cow-orderbook-only.sh. All green.

AI Assistance

Implemented with Claude Code.

Closes #544