[codex] Add Alloy WebSocket subscriber

[KaiCode2]

Summary

• Make AlloySubscriber drive WebSocket/pubsub subscriptions by default under reactive-ws, with HTTP polling exported through opt-in reactive-polling.
• Add source-specific WebSocket reconnect handling with an immediate first retry, three attempts by default, log gap backfill from the last seen block, and recent canonical input duplicate suppression.
• Add the live AMM probe example, subscriber tests, feature-gating coverage, README updates, and changelog notes.

Validation

• cargo test
• cargo test --no-default-features
• cargo test --no-default-features --features reactive,reactive-polling
• cargo test --all-features --test reactive_alloy_subscriber
• cargo clippy --all-targets --no-deps -- -D warnings
• cargo clippy --no-default-features --features reactive,reactive-polling --all-targets --no-deps -- -D warnings
• cargo clippy --all-features --all-targets --no-deps -- -D warnings
• RUSTDOCFLAGS="-D warnings" cargo doc --no-deps
• RUSTDOCFLAGS="-D warnings" cargo doc --no-deps --no-default-features --features reactive,reactive-polling
• cargo fmt --all --check
• git diff --check
• Live WS AMM probe against mainnet observed subscribed AMM logs with reconnect state enabled.