chore: pleasure clippy

```console
$ cargo clippy
   Compiling picodata v0.1.0 (/home/rosik/w/picodata)
warning: 'tarantool-sys/patches-applied' exists, so patching step is
skipped
warning: single-character string constant used as pattern
   --> src/args.rs:194:47
    |
194 |     let (host, port) = match text.rsplit_once(":") {
    |                                               ^^^ help: try using
a `char` instead: `':'`
    |
    = note: `#[warn(clippy::single_char_pattern)]` on by default
    = help: for further information visit
https://rust-lang.github.io/rust-clippy/master/index.html#single_char_pattern

warning: called `cloned().next()` on an `Iterator`. It may be more
efficient to call `next().cloned()` instead
   --> src/discovery.rs:154:27
    |
154 |                 let res =
    peers.difference(&self.visited).cloned().next();
    |
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try this:
`peers.difference(&self.visited).next().cloned()`
    |
    = note: `#[warn(clippy::iter_overeager_cloned)]` on by default
    = help: for further information visit
https://rust-lang.github.io/rust-clippy/master/index.html#iter_overeager_cloned

warning: you seem to be trying to use `match` for destructuring a single
pattern. Consider using `if let`
  --> src/ipc.rs:27:9
   |
27 | /         match rmp_serde::encode::write(&mut self.fd, msg) {
28 | |             Err(e) => tlog!(Error, "ipc error: {e}"),
29 | |             Ok(()) => (),
30 | |         }
   | |_________^ help: try this: `if let Err(e) =
rmp_serde::encode::write(&mut self.fd, msg) { tlog!(Error, "ipc error:
{e}") }`
   |
   = note: `#[warn(clippy::single_match)]` on by default
   = help: for further information visit
https://rust-lang.github.io/rust-clippy/master/index.html#single_match

warning: `picodata` (bin "picodata") generated 3 warnings
    Finished dev [unoptimized + debuginfo] target(s) in 1.41s
```