feat: use lockfiles to determine if daemon is running

[paperluigis]

Description

This PR makes the daemon create and lock a file next to the IPC socket (ex. "/run/user/1000/eww-server_f12a67507f690016.lock"). It also makes the program check if the daemon is running by seeing if the file is locked by another process, instead of sending a ping command to the daemon.

This will fix #255, where a timeout in sending an open command over IPC caused the program to create a new daemon, leading to "zombie windows" being left over by the existing daemon.
This will also hopefully make the daemon launch a bit quicker when started as eww open bar.

Additional Notes

i haven't tested this on platforms other than linux

is this a feature or a fix?

this uses the std::fs::File::try_lock method which is cleaner but only available in rust 1.89.0 and above; i have an alternative implementation that uses nix::fcntl::Flock instead, should i submit the alternative instead?

Checklist

Please make sure you can check all the boxes that apply to this PR.

• All widgets I've added are correctly documented.
• I added my changes to CHANGELOG.md, if appropriate.
• The documentation in the docs/content/main directory has been adjusted to reflect my changes.
• I used cargo fmt to automatically format all code before committing

[w-lfchen]

since eww has a rust-toolchain.toml file that currently is set to 1.81, this pr will break anything relying on that file to determine the rust version to compile eww with due to using newer apis.
in my opinion, the right move here would be updating said file and fixing issues that may arise in the process.
i currently don't really have time to do so for personal reasons, would love to do it otherwise.

[paperluigis]

is there anything i should look out for after doing so? do i just have to make sure it still compiles?

[w-lfchen]

there could be new warnings or lints