fix: properly check if metamask is installed

[chalabi2]

ISSUE

The cosmos-extension-metamask wallet does not properly check if metamask is installed or not.

SUMMARY

In the Leap metamask snap extension we properly check for the metamask window with

interface MetamaskWindow {
  ethereum?: {
    isMetaMask?: boolean;
  };
}

export const isMetamaskInstalled: () => Promise<boolean> = async () => {
  if (typeof window === 'undefined') {
    return false;
  }

  const ethereum = (window as MetamaskWindow).ethereum;

  if (ethereum?.isMetaMask) {
    return true;
  }

  if (document.readyState === 'complete') {
    if (ethereum?.isMetaMask) {
      return true;
    } else {
      throw ClientNotExistError;
    }
  }

But in the cosmos-extension we do not

interface SnapWindow {
cosmos?: CosmosSnap;
}

export const getSnapProviderFromExtension: () => Promise<
CosmosSnap | undefined
> = async () => {
if (typeof window === 'undefined') {
  return void 0;
}

const cosmos = (window as SnapWindow).cosmos;

if (cosmos) {
  return cosmos;
}

if (document.readyState === 'complete') {
  if (cosmos) {
    return cosmos;
  } else {
    throw ClientNotExistError;
  }
}

[fmorency]

cc @pyramation