Fixes all warnings when `-require-explicit-sendable` flag is enabled and
enables the flag on macOS CI.
### Motivation:
We want to ensure our public API is either explicitly marked as
`Sendable` or not.
### Modifications:
Marked appropriate public types as `Sendable`, or explicitly defined
their conformance to the `Sendable` protocol as unavailable.
### Result:
We can now enable `-require-explicit-sendable` compiler flag in our
codebase.
Add functions for reading and writing length-prefixed data with
customizable encodings for the length, particularly for quic
variable-length integers (RFC 9000)
### Motivation:
Many protocols require us to write data and then prefix that data with
its length. But each protocol has a different way of encoding the
length. This PR introduces general purpose functions which can be
extended for different encoding strategies
### Modifications:
Create a new protocol which defines how to encode an integer
Implement this protocol for QUIC
Provide functions on bytebuffer for writing length-prefixed buffers,
strings or bytes
Rafael Cepeda
hamzahrmalik