rust: pin-init: examples: mark as `#[inline]` all `From::from()`s for `Error`

rust: pin-init: examples: mark as `#[inline]` all `From::from()`s for `Error`

There was a recent request in kernel [1] to mark as `#[inline]` the
simple `From::from()` functions implemented for `Error`.

Thus mark all of the existing

    impl From<...> for Error {
        fn from(err: ...) -> Self {
            ...
        }
    }

functions as `#[inline]`.

While in pin-init crate the relevant code is just examples, it
nevertheless does not hurt to use good practice for them.

Suggested-by: Gary Guo <gary@garyguo.net>
Link: https://lore.kernel.org/all/8403c8b7a832b5274743816eb77abfa4@garyguo.net/
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
[ Reworded commit message - Gary ]
Link: https://patch.msgid.link/20260428-pin-init-sync-v1-1-07f9bd3859fb@garyguo.net
Signed-off-by: Gary Guo <gary@garyguo.net>