* Add support for streaming delimited messages
This allows developers to easily dump and load multiple messages
from a stream in a way that is compatible with official
protobuf implementations (such as Java's
`MessageLite#writeDelimitedTo(...)`).
* Add Java compatibility tests for streaming
These tests stream data such as messages to output files, have a
Java binary read them and then write them back using the
`protobuf-java` functions, and then read them back in on the Python
side to check that the returned data is as expected. This checks
that the official Java implementation (and so any other matching
implementations) can properly parse outputs from Betterproto, and
vice-versa, ensuring compatibility in these functions between the
two.
* Replace `xxxxableBuffer` with `SupportsXxxx`
