Refactor to Cargo Workspace (#129)

* Refactor project into a Cargo workspace with distinct packages

- Created a root `Cargo.toml` defining a workspace.
- Moved `src/types` and `src/utils` into a new `pwsp-lib` crate for shared logic.
- Split binaries into their own crates: `pwsp-daemon`, `pwsp-cli`, and `pwsp-gui`.
- Shifted all dependencies into `[workspace.dependencies]` for centralized version management.
- Updated import paths across all crates (e.g. from `pwsp::` to `pwsp_lib::`).
- Updated build scripts, GitHub actions, Flatpak manifest, and AUR PKGBUILD to support the new workspace structure.
- Ensured no core application logic was altered.

Co-authored-by: arabianq <55220741+arabianq@users.noreply.github.com>

* Fix cargo-deb build process in GitHub actions for workspace architecture

Co-authored-by: arabianq <55220741+arabianq@users.noreply.github.com>

* Fix cargo-deb asset discovery by using exact target/release paths

Co-authored-by: arabianq <55220741+arabianq@users.noreply.github.com>

* refactor deps in Cargo.toml files

* fix incorrect assets path

---------

Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>

pwsp-gui/assets/pwsp-daemon.service

@@ -0,0 +1,11 @@
+[Unit]
+Description=Pipewire Soundpad Daemon
+After=pipewire.service
+
+[Service]
+ExecStart=/usr/bin/pwsp-daemon
+Restart=no
+RuntimeDirectory=pwsp
+
+[Install]
+WantedBy=default.target