Polling eth_blockNumber gives incorrect results

[jannikluhn]

Describe the bug

Polling eth_blockNumber gives incorrect results when Metamask is connected to a local dev chain. Presumably, there's a cache that is only updated every ~20s. This is too infrequent for dev chains with, say, a 2s block time.

Steps to reproduce

1. Start a local dev chain, e.g., with geth or ganache.
2. Connect metamask to this chain
3. Run the following command repeatedly on a metamask-connected site: await window.ethereum.request({method: "eth_blockNumber", params: []})

Expected behavior

eth_blockNumber should always return the current block number.

Browser details (please complete the following information):

• OS: Linux
• Browser: Mozilla Firefox 86.0
• MetaMask Version: 9.1.0

Additional context

curling the node directly always gives the right answer.

[alexdupre]

See #13302 for additional context