aw-server-rust: fix failing build due to removed unstable feature

Rust compiler plugins have been entirely removed after having been
deprecated for years [1]. This caused the build of `aw-server-rust`
to break because its `aw-server` crate still contained the respective
crate attribute to enable the feature.

This attribute has already been removed upstream along with other
no longer used unstable feature opt-ins [2]. This change pulls in
the respective commit with `fetchpatch` and filters it down to
only the changes in `aw-server/src/lib.rs`, which fixes the build
for now. The patch should be removable with the next release
(0.12.3).

[1]: rust-lang/rust#116412
[2]: https://github.com/ActivityWatch/aw-server-rust/commit/e1cd761d2f0a9309eb851b59732c2567a7ae2d3a.patch

Author: mfrischknecht

pkgs/applications/office/activitywatch/default.nix

@@ -1,5 +1,6 @@
 { lib
 , fetchFromGitHub
+, fetchpatch
 , rustPlatform
 , makeWrapper
 , pkg-config
@@ -164,6 +165,14 @@ rec {
         src = ./override-version.patch;
         version = sources.rev;
       })
+
+      # Can be removed with release 0.12.3
+      (fetchpatch {
+        name = "remove-unused-unstable-features.patch";
+        url = "https://github.com/ActivityWatch/aw-server-rust/commit/e1cd761d2f0a9309eb851b59732c2567a7ae2d3a.patch";
+        hash = "sha256-wP+3XZDkr148XY5b8RV3obuLczAFBE3FhaYPqnmmGcU=";
+        includes = [ "aw-server/src/lib.rs" ];
+      })
     ];
 
     nativeBuildInputs = [