chore: fix unnecessary usage of () in Redis commands

[defiberrys]

I found an issue where () was incorrectly used in the following lines:

() = conn.set(&key, data.clone()).await?;

and

() = conn.publish(&key, "updated").await?;

This usage of () was not needed, as it doesn't serve any purpose here. The code has been corrected to simply call the methods without the unnecessary assignment:

conn.set(&key, data.clone()).await?;

and

conn.publish(&key, "updated").await?;

These changes ensure that the Redis commands are executed correctly.

[benalleng]

Make sure to run the linter with ./contrib/lint.sh when pushing changes, we have the flag -D warnings set so any warning is considered a failure!
I found this warning.

warning: this function depends on never type fallback being `()`
  --> payjoin-directory/src/db.rs:74:5
   |
74 | /     async fn push(
75 | |         &self,
76 | |         subdirectory_id: &ShortId,
77 | |         channel_type: &str,
78 | |         data: Vec<u8>,
79 | |     ) -> Result<()> {
   | |___________________^
   |
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in Rust 2024 and in a future release in all editions!
   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/never-type-fallback.html>
   = help: specify the types explicitly
note: in edition 2024, the requirement `!: FromRedisValue` will fail
  --> payjoin-directory/src/db.rs:82:14
   |
82 |         conn.set(&key, data.clone()).await?;
   |              ^^^
   = note: `#[warn(dependency_on_unit_never_type_fallback)]` on by default

I think we can find a cleaner way to handle ignoring the Result here but perhaps there was more thought to the inclusion of these () than it might have seemed.

[coveralls]

Pull Request Test Coverage Report for Build 14007606865

Details

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.03%) to 80.378%

---

Files with Coverage Reduction	New Missed Lines	%
payjoin/src/send/mod.rs	2	94.31%

Totals
Change from base Build 14002185069:	-0.03%
Covered Lines:	4846
Relevant Lines:	6029

---

💛 - Coveralls

[DanGould]

I think we can find a cleaner way to handle ignoring the Result here

The syntax using ? means that the Result is explicitly handled by propagating an error and returning the unit type for Ok. I don't think I'd describe that as being ignored

[benalleng]

Thats a fair clarification, I guess we are just constraining the type with () = TBH I was a little confused about what the warning was trying to tell us.., If I had to guess I'm going to assume we've already gone through all of these resources already seeing as spacebear already made this commit 219296f but I figure they are a good read to clarify why this code is the way it is.

https://users.rust-lang.org/t/this-function-depends-on-never-type-fallback-being/120158/6

rust-lang/rust#126466

rust-lang/rust#123748 (comment)

https://doc.rust-lang.org/edition-guide/rust-2024/never-type-fallback.html

Long story short the usage of ? makes this code infer to either a () or ! depending on the never type fallback. Because our code expects returning the RedisResult with a generic T we should set it to be () = conn.set(&key, data.clone()).await?; so that we don't fallback to the never ! type.