enable async calls

[jingyi-zhao-01]

Is your feature request related to a problem? Please describe. https://polygon.io/docs/rest/options/snapshots/option-contract-snapshot

• client.get_snapshot_option is sync,cannot leverage coroutine for multiple asynchrounus fetching.
• it's very slow when fetching each one by one.

Describe the solution you'd like

• Enable async call of this funtion version so people cacn leverage ccouroutine.

tasks = [
        client.get_contract_snapshot_async(underlying_asset, contract.ticker)
        for contract in contracts
    ]

    return await asyncio.gather(*tasks)

[charlielidbury]

Could also do it like OpenAI where there is just a whole separate client, where everything is async.

Keeps the existing API unchanged, and people probably don't want to do both sync and async at the same time