Add SimpleSwap swap support

[andreykr-simpleswap]

CHANGELOG

Does this branch warrant an entry to the CHANGELOG?

• Yes

Dependencies

none

Description

Context

This PR adds SimpleSwap (https://simpleswap.io) as a centralized swap
provider. We're the SimpleSwap engineering team — the plugin is built
against our public API v3, following CREATING_AN_EXCHANGE_PLUGIN.md and
the central template.

Changes

• src/swap/central/simpleswap.ts — the plugin. Tries a fixed-rate
  quote first and falls back to a float rate. Supports both quote
  directions, checks limits via our ranges endpoint before creating an
  order, and maps API errors to the Edge error types. max quotes use
  a local probe for fee estimation, so no orders are created and
  abandoned along the way.
• Chain mappings under src/mappings/ and a synchronizer under
  scripts/, generated from our live currency list with mapctl.
• Plugin registration in src/index.ts.
• test/simpleswap.test.ts — covers the mapping for every
  EdgeCurrencyPluginId, both quote directions, limit errors, the
  fixed-to-float fallback, currency code transcription, and the max
  path.

Init options: SIMPLESWAP_INIT: { "apiKey": "..." }. The factory
throws on an empty key, so builds without the key just skip the plugin.

Verification

• npm run verify passes.
• Quotes and order creation tested end to end against our sandbox in
  both directions: deposit addresses and order URIs come back correct.
• Ran the full app from edge-react-gui in the iOS simulator: the plugin
  builds, shows up in Exchange Settings, quotes btc->eth and creates
  live orders on the sandbox.

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Note

Medium Risk
New third-party swap path controls deposit amounts and addresses; mistakes could misquote or strand orders, though behavior mirrors other central plugins and is heavily tested.

Overview
Adds SimpleSwap as a new centralized swap provider, wired into the plugin registry and documented in the changelog.

The new plugin talks to SimpleSwap API v3: it checks ranges, fetches estimates, then creates an exchange and builds the deposit spendInfo (including deposit memos when extraIdFrom is present). Quotes prefer fixed rates and fall back to floating when fixed fails, with error ranking so limit/permission/pair errors are not masked by transient failures. Max swaps use a local fee probe (skipChecks spend to the user’s own address) so only one live order is created. Chain and ticker mapping comes from generated simpleswap maps plus a small currency-code transcription table; mapctl gains a synchronizer and SIMPLESWAP_API_KEY config.

Tests cover mappings for every EdgeCurrencyPluginId, both quote directions, limits, fixed→float fallback, max-quote behavior, and amount rounding guards.

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