{examples,tests}/rust: cargo update

This restores compatibility with current nightlies by using the latest
coap-message version (after a nightly-only feature that uses saw a late
change), and also removes obstacles for use with stable Rust 1.59 (in
unrelated parts; the CoAP example is still nightly-only).

Contributes-To: https://github.com/RIOT-OS/RIOT/issues/17526

examples/rust-gcoap/Cargo.toml

@@ -12,5 +12,5 @@ crate-type = ["staticlib"]
 riot-wrappers = { version = "^0.7", features = [ "with_coap_message", "with_coap_handler" ] }
 
 coap-message-demos = { git = "https://gitlab.com/chrysn/coap-message-demos/", default-features = false }
-coap-handler-implementations = "0.1"
+coap-handler-implementations = "0.3"
 riot-coap-handler-demos = { git = "https://gitlab.com/etonomy/riot-module-examples/", features = [ "vfs" ] }