Add n.exchange centralized swap integration

Integrate n.exchange as a centralized swap provider supporting
multiple networks and tokens. The implementation uses contract
addresses for token identification, eliminating the need for
currency code mapping. This approach provides better support for
tokens and aligns with API requirements.

The integration includes support for native currencies and ERC20
tokens across major networks including Ethereum, Polygon, Base,
Arbitrum, Optimism, BSC, and others. The plugin handles rate
queries, order creation, and payment processing through the
n.exchange API v2.

Additional changes include mapctl tooling for automatic provider
mappings and updates to existing swap plugins to use the new
mapping system.

Author: MMrj9

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ## Unreleased
 
+- added: n.exchange centralized swap integration with support for multiple networks and tokens using contract address-based identification
+
 ## 2.40.3 (2025-12-29)
 
 - fixed: Fix Rango EVM approval address

src/index.ts

@@ -7,6 +7,7 @@ import { makeChangeNowPlugin } from './swap/central/changenow'
 import { makeExolixPlugin } from './swap/central/exolix'
 import { makeGodexPlugin } from './swap/central/godex'
 import { makeLetsExchangePlugin } from './swap/central/letsexchange'
+import { makeNexchangePlugin } from './swap/central/nexchange'
 import { makeSideshiftPlugin } from './swap/central/sideshift'
 import { makeSwapuzPlugin } from './swap/central/swapuz'
 import { make0xGaslessPlugin } from './swap/defi/0x/0xGasless'
@@ -35,6 +36,7 @@ const plugins = {
   godex: makeGodexPlugin,
   letsexchange: makeLetsExchangePlugin,
   lifi: makeLifiPlugin,
+  nexchange: makeNexchangePlugin,
   rango: makeRangoPlugin,
   sideshift: makeSideshiftPlugin,
   spookySwap: makeSpookySwapPlugin,