ec-test-app: Add serial source

[kurtjd]

This PR does a few things:

• Adds serial as a Source, which allows the app to talk directly to a dev platform in user-space (over a COM port for example). Can be useful for testing services without needing to worry about FFA and whatnot.
• Fixes some clippy warnings introduced from needing to bump MSRV
• Some minor refactoring to use the message structs defined by the crates in embedded-services

Tested this on the dev-imxrt platform and works pretty well.

Can run with:
cargo run --release --features serial <COM#> none [baud]

Baud rate is an optional argument and can be omitted since I have it set to default to 115200 which the dev platforms use.

[philgweber]

Will have to think about the transport and integrating with FFA and secure world so we have the ability to redirect messages through either path.

[kurtjd]

Will have to think about the transport and integrating with FFA and secure world so we have the ability to redirect messages through either path.

So I was thinking this can be used as an alternative to going through FFA when someone jsut wants to quickly connect to a board and do some testing of the services. In my mind I imagined this app will just select the acpi source if it wants to talk to FFA, and whether FFA goes through uart or eSPI from the apps perspective shouldn't matter. Does that seem similar to what you were thinking?

[williampMSFT]

[kurtjd]

Will wait for #41 to merge, then update this PR to implement RtcSource for serial.

[kurtjd]

Updated to include Time and Alarm Service since #41 was merged.

[kurtjd]

@jerrysxie @tullom Please review when you have a chance

[tullom]

Thank you for the ping, tested this with the rt685 evk board and the data was updating! Great job with this!

[kurtjd]

Thank you for the ping, tested this with the rt685 evk board and the data was updating! Great job with this!

Thank you! :)