feat!: use FsCodec.Encoded bodies

[bartelink]

Removes two problems:

• Feeds that support encoding (.e.. DynamoStore) used to have to uncompress on reading, wasting memory
• CosmosStore used to pass JsonElement verbatim, but not pass the encoding. Equinox.CosmosStore v 4.1.0 requires the encoding value to be passed as a JSON String can now represent either Deflate or Brotli encoded data depending on the encoding stored in D or M alongside the body field