feat(polymarket): CLOB V2 migration — hard-cut to V2 contracts and EIP-712 struct

Implements full Polymarket CLOB V2 cutover (go-live 2026-04-28 ~11:00 UTC):

- EIP-712 Order struct: drop taker/nonce/feeRateBps/expiration from signed types;
  add timestamp(uint256 ms), metadata(bytes32), builder(bytes32)
- Domain version '1' → '2' (mainnet only; Amoy testnet keeps '1' for V1 contracts)
- V2 mainnet exchange/negRiskExchange contracts + pUSD/usdce/onramp/offramp addresses
- expiration kept in POST /order wire body only (excluded from signed struct per V2 spec)
- feeSchedule parsing from Gamma market payload (Mar 31 2026 change)
- Keyset cursor pagination in fetchMarkets/fetchOrders/fetchTrades (Apr 10 2026)
- wrapCollateral(): thin helper to wrap USDC.e → pUSD via CollateralOnramp.wrap()
- builderCode bytes32 pass-through + length validation (66 chars, 0x-prefixed)
- getSignatureType(): honour caller params.signatureType/signature_type override
- Fix extend() order in fetchOrders/fetchTrades so loop cursor wins over params
- salt = orderTimestamp (unified from separate milliseconds() calls)
- pro/polymarket.ts: declare missing marketUpdates property

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: Herklos

package-lock.json

@@ -1,6 +1,6 @@
 {
   "name": "ccxt",
-  "version": "4.5.40",
+  "version": "4.5.41",
   "description": "A cryptocurrency trading API with more than 100 exchanges in JavaScript / TypeScript / Python / C# / PHP / Go",
   "unpkg": "dist/ccxt.browser.min.js",
   "type": "module",

package.json

@@ -10,10 +10,12 @@ import { Exchange as _Exchange } from '../base/Exchange.js';
 
 interface Exchange {
     gammaPublicGetMarkets (params?: {}): Promise<implicitReturnType>;
+    gammaPublicGetMarketsKeyset (params?: {}): Promise<implicitReturnType>;
     gammaPublicGetMarketsId (params?: {}): Promise<implicitReturnType>;
     gammaPublicGetMarketsIdTags (params?: {}): Promise<implicitReturnType>;
     gammaPublicGetMarketsSlugSlug (params?: {}): Promise<implicitReturnType>;
     gammaPublicGetEvents (params?: {}): Promise<implicitReturnType>;
+    gammaPublicGetEventsKeyset (params?: {}): Promise<implicitReturnType>;
     gammaPublicGetEventsId (params?: {}): Promise<implicitReturnType>;
     gammaPublicGetSeries (params?: {}): Promise<implicitReturnType>;
     gammaPublicGetSeriesId (params?: {}): Promise<implicitReturnType>;