Allow for compressed graph payloads

We should support compressed payloads e.g. once we have graph chunks https://github.com/tinygraph/tinygraphio/issues/7 we could add a flag to each chunk if the payload is raw or compressed; take inspiration from [this spec](https://github.com/protomaps/PMTiles/blob/252023ea29d8ce8ba816d7791e8e6a8b1252abd0/spec/v3/spec.md#33-compression).