This change removes lots of pointless string and custom format parsing code and instead relies on protobuf to do the thing. JSON is still an option thanks to proto3-generated output.
- Refactored ObjectID to use protobuf
- Indirect blocks to use protobuf (in the form of seek table)
- Added generic proto stream reader and writer
- ObjectIDFormat became proto enum
Also:
- fixed major issue where indirect object ID entries were not encrypted, since they were storing block IDs and not object IDs.
- dropped support for majority of formats, only supporting HMAC-{SHA256,SHA512,SHA512_384} hashes with AES256.
This produces object IDs of 32 or 64 characters long.
- changed how pretty-printing works for 'kopia show'
