rust: Bring in fugit library

The fugit crate implements tick-based timers, providing a `Duration` and
`Instant` type that we can use for timeouts.

This is an external crate, covered under the Apache-2.0 or MIT license.
This will need to be vendored due to Rust policies.

Signed-off-by: David Brown <[email protected]>

Author: d3zd3z

lib/rust/zephyr/Cargo.toml

@@ -12,6 +12,9 @@ Functionality for Rust-based applications that run on Zephyr.
 [dependencies]
 zephyr-sys = { version = "0.1.0", path = "../zephyr-sys" }
 
+[dependencies.fugit]
+version = "0.3.7"
+
 # These are needed at build time.
 # Whether these need to be vendored is an open question.  They are not
 # used by the core Zephyr tree, but are needed by zephyr applications.