nightly warning: unused `ControlFlow` that must be used

[BenWiederhake]

When compiling with nightly (cargo 1.88.0-nightly 2025-03-26 or newer, probably older as well), we get some compilation warnings:

warning: unused `ControlFlow` that must be used
   --> src/uucore/src/lib/features/format/mod.rs:281:9
    |
281 |         item?.write(&mut writer, &mut args)?;
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: `#[warn(unused_must_use)]` on by default
help: use `let _ = ...` to ignore the resulting value
    |
281 |         let _ = item?.write(&mut writer, &mut args)?;
    |         +++++++

warning: unused `ControlFlow` that must be used
   --> src/uu/echo/src/echo.rs:153:17
    |
153 | /                 match item {
154 | |                     EscapedChar::End => return Ok(()),
155 | |                     c => c.write(&mut *stdout_lock)?,
156 | |                 };
    | |_________________^
    |
    = note: `#[warn(unused_must_use)]` on by default
help: use `let _ = ...` to ignore the resulting value
    |
153 |                 let _ = match item {
    |                 +++++++

It seems that there have been some changes to the inner workings of the compiler: rust-lang/rust#137449

I'm not quite sure how to deal with this, but it seems that this warning will make it's way into stable eventually I guess, so let's "fix" this issue? However, in both cases I don't fully understand why that is even necessary, so I don't trust the compiler-suggested code.

[tertsdiepraam]

The ControlFlow dictated whether the formatting should exit early, which happens if \0 was passed I think. Both of these cases might need to return in that case, but we'd have to test to see what GNU does.