refactor: move Account.get_exitable_utxos/1 into watcher security

[unnawut]

Overview

This PR moves OMG.WatcherInfo.API.Account.get_exitable_utxos/1 to OMG.Watcher.

Thanks to @jrhite for spotting this boundary breach:

@jrhite: Just ran across this code in WatcherInfo. Seems strange that it's in Info using OMG.DB. Curious why it's in Info, what's the rationale for it? There's a simple query for the same info in db/transaction.ex, but currently it only filters unspent or unexited txoutputs. It could be extended to also filter out txoutputs in an IFE state or other various scenarios.

Thanks!

  @doc """
  Gets all utxos belonging to the given address.
  Slow operation, compatible with security-critical.
  """
  # TODO this seems weird and a breach of decoupling
  @spec get_exitable_utxos(OMG.Crypto.address_t()) :: list(OMG.State.Core.exitable_utxos())
  def get_exitable_utxos(address) do
    # OMG.DB.utxos() takes a while.
    {:ok, utxos} = OMG.DB.utxos()
    OMG.State.Core.standard_exitable_utxos(utxos, address)
  end

Changes

• Move OMG.WatcherInfo.API.Account.get_exitable_utxos/1 to OMG.Watcher.API.Account
• Tests

Testing

These Too Should All Pass:

$ mix test test/omg_watcher/api/account_test.exs
$ mix test test/omg_watcher_rpc/web/controllers/account_test.exs

[coveralls]

Coverage remained the same at 88.138% when pulling da3b4e6 on unnawut/move-watcher-security-function into 6f4d00f on master.