Support schema/migrations for binary encoding

[tmpfs]

Possibly use Protobuf/CapNProto/Thrift or Avro.

So that we could change the binary encoding for vaults in future versions with backwards compatibility and offer tools to migrate from binary encoding versions.

[tmpfs]

My current thinking on this is that we leverage webassembly to solve this problem.

Move the encoder and decoder routines to WASM modules and then we can bundle different webassembly modules for different versions of the binary schema which can be used to migrate between versions.

This will likely add significant overhead to the encoding and decoding of vaults and to support VaultFileAccess would need to be wasm32-wasi compatible.

For the planned plugin architecture we will need a webassembly runtime so it is already expected that we add that dependency.