Add user-directed Router

[1kresh]

Summary

• Adds the ownerless Router contract for atomic user-directed multi-solver execution.
• Defines SwapCall as exactly (adapter, amountIn, data).
• For each leg, checks that the target is registered by LIQUID_LANE_ADAPTER_FACTORY, transfers input directly from the caller to that adapter, and invokes the supplied calldata inline.
• After all legs, transfers declared ERC-20 outputs to recipients in caller-supplied order.
• Keeps the no-deadline and deadline execute overloads, constructor factory validation, SafeERC20, ReentrancyGuard, deployment script, documentation, and Foundry tests.

Deliberately minimal trust boundary

• The Router does not inspect adapter selectors or signatures and therefore supports both signed-swap and discounted-swap calldata.
• It does not validate amount sums, token/recipient fields, input consumption, balance deltas, or surplus.
• Output transfers use the Router's current balances; undeclared surplus remains in the Router.
• Registered adapters remain responsible for selector, signature, nonce, quote, recipient/caller, and deadline validation.
• Any failed registry lookup, transfer, adapter call, output transfer, reentrant call, or expired Router deadline reverts the whole batch atomically.

Companion PRs: symbioticfi/rfq-backend#292 and symbioticfi/vault-solver#116.

Verification

• Solidity 0.8.28 Foundry suite: 37 tests passing
• Router fuzz test: 10,000 runs
• forge fmt --check, focused lint, and build pass in the dependency harness