feat(rfq): add Euclid Protocol RFQ provider

[EliasSalameh]

Adds rfq:euclid as an RFQ liquidity source. Euclid's liquidity lives on its own app chain (VSL); the Euclid RFQ gateway quotes that depth as indicative price levels and settles fills atomically on the taker's chain from pre-positioned maker inventory.

• tycho-simulation: EuclidClient (public WebSocket levels stream as full-state JSON frames + HTTP firm-quote endpoint with optional x-api-key), EuclidState (ProtocolSim + IndicativelyPriced over bid/ask ladders), decoder, builder, and EUCLID_API_URL/EUCLID_API_KEY configuration. Mirrors the Bebop integration structure.
• tycho-execution: EuclidSwapEncoder (binding quote at encode time; packs token_in | token_out | tx_to | partial_fill_offset | original amount | calldata) and EuclidExecutor.sol. Euclid orders are maker-signed 1inch limit-order-protocol v3 RFQ orders settled through the 1inch Aggregation Router v5 (fillOrderRFQTo); the executor pins that router, allowlists the single fill selector, and patches the filled taker amount downward only. Foundry tests sign real orders with a test key and fill them through the live router on a mainnet fork, covering full and partial fills plus target/selector rejection.
• rfq_quickstart: EUCLID_ENABLED wiring + README.

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[EliasSalameh]

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