title: Vyper how to convert uint256 to String?
body: <p>I need to convert a uint256 to String in vyper, I notice that theres something similar on Solidity (Taken from <a href="https://docs.opensea.io/docs/metadata-standards" rel="noreferrer">OpenSea's docs</a>):</p>
  <pre><code>/**
     * @dev Returns an URI for a given token ID
     */
    function tokenURI(uint256 _tokenId) public view returns (string) {
      return Strings.strConcat(
          baseTokenURI(),
          Strings.uint2str(_tokenId)
      );
    }
  </code></pre>
  <p>There's a method called &quot;Strings.uint2str()&quot;, is there something equivalent in Vyper?</p>