Add ability to use Rust formatted strings with cFE syslog, events

[zec]

Right now, with the use of printf-wrap, n2o4 has decent support for printf(3)-type formatting with syslog entries and events. However, Rust has its own string-formatting system. It would be good to support using that instead when making syslog entries or events for a more Rustic experience.

Some things that may come in handy when creating that:

core::write
core::fmt::Write
core::format_args

In particular, implementing Write for a "[u8; N] plus index-into-buffer" type would allow all this to be done without heap allocations.