nix: Clean up build (#27881)

- bump our livekit version to include a fix for a crane bug (TODO: add
link when an issue is filed on crane)
- switch to a clang stdenv for both linux and macos
- manually unify versions of our notify crate
- remove old linker flags which were only needed for livekit
- fix an issue where RUSTFLAGS shadowed the rustflags from cargo configs

Release Notes:

- N/A

.cargo/config.toml

@@ -14,10 +14,10 @@ linker = "clang"
 rustflags = ["-C", "link-arg=-fuse-ld=mold"]
 
 [target.aarch64-apple-darwin]
-rustflags = ["-C", "link-args=-Objc -all_load"]
+rustflags = ["-C", "link-args=-all_load"]
 
 [target.x86_64-apple-darwin]
-rustflags = ["-C", "link-args=-Objc -all_load"]
+rustflags = ["-C", "link-args=-all_load"]
 
 [target.'cfg(target_os = "windows")']
 rustflags = [