Introduce FailoverRpcProvider that switches between providers in case of a failure of one of them

[denbite]

Pre-flight checklist

• I have read the Contributing Guidelines on pull requests.
• Commit messages follow the conventional commits spec
• If this is a code change: I have written unit tests.
• If this changes code in a published package: I have run pnpm changeset to create a changeset JSON document appropriate for this change.
• If this is a new API or substantial change: the PR has an accompanying issue (closes #0000) and the maintainers have approved on my working plan.

Motivation

RPC providers can experience intermittent downtime, connectivity issues, or rate limits that cause client transactions to fail. This could have been prevented if near-api-js had the FailoverRpcProvider that supports multiple RPC providers.

const jsonProviders = [
  new JsonRpcProvider({
    url: 'https://rpc.mainnet.near.org',
  }),
  new JsonRpcProvider(
    {
      url: 'https://another-rpc.cloud.com',
      headers: { 'X-Api-Key': 'some string' },
    },
    { retries: 3, backoff: 2, wait: 500 }
  ),
];
const provider = new FailoverRpcProvider(jsonProviders);

await connect({
  networkId: 'mainnet',
  provider: provider,
  // this isn't used if `provider` is specified, but is still required for backward compativility
  nodeUrl: 'https://rpc.mainnet.near.org',
});

Test Plan

Related issues/PRs

#1216
#760

Discussion #733

[changeset-bot]

🦋 Changeset detected

Latest commit: 6ad04ef

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 5 packages

Name	Type
@near-js/accounts	Minor
@near-js/providers	Minor
@near-js/wallet-account	Minor
@near-js/cookbook	Patch
near-api-js	Patch

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