build(nix): add flake.nix for cross-compilation from darwin and linux

I was getting really tired of having to switch between display inputs to
different platform-specific machines to be able to make and test changes
on komorebi for Windows and komorebi for Mac.

With this commit, the `flake.nix` provides a Nix devShell and crane
build for users to make and validate changes with `cargo check`, `cargo
clippy` and `cargo build` with the Windows MSVC toolchain on Linux and
macOS.

komorebic-no-console/Cargo.toml

@@ -8,5 +8,3 @@ edition = "2024"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
-
-