Transition heatmap granule encoding to binary

[erlewa]

Heatmap Granule data is currently being sent to the client as a json string. By switching this encoding to binary using bincode we can dramatically reduce the size of transferred data.

• Updated heatmap-client/src/ingest/request.rs
  • Swapped serde_json::from_str to bincode::decode_from_slice
  • Tidied up code for requesting heatmap granule data
• Updated heatmap-servcie/src/query.rs
  • Swapped Serde Serialize to use Bincode Encode. Serde Serialize and Deserialize traits are still implemented as the redis cache relies on them, something that I will look into fixing if I have time

[erlewa]

This PR was consolidated into #58