radicle-tauri/build: Allow Specifying Version via `GIT_HEAD` — radicle-desktop

This now allows setting GIT_HEAD “from the outside” and will gracefully fall back to “unknown” in case there’s any issue figuring out what HEAD refers to.

Also tells Nix about it and bumps MSRV to an unsurprisingly old version.

 authors = ["Rudolfs Osins <rudolfs@osins.org>", "Sebastian Martinez <me@sebastinez.dev>"]
 license = "MIT OR Apache-2.0"
 edition = "2021"
 rust-version = "1.70"
 rust-version = "1.77"
 publish = false
 [lib]

 use std::env;
 use std::process::Command;
 fn main() {
     let output = Command::new("git")
         .args(["rev-parse", "--short", "HEAD"])
         .output()
         .expect("failed to execute git");
     let git_head = String::from_utf8(output.stdout).unwrap();
     println!("cargo:rustc-env=GIT_HEAD={}", git_head);
     let head = env::var("GIT_HEAD").unwrap_or_else(|_| {
         Command::new("git")
             .args(["rev-parse", "--short", "HEAD"])
             .output()
             .map(|output| String::from_utf8(output.stdout).expect("output from Git is UTF-8"))
             .unwrap_or("unknown".into())
     });
     println!("cargo::rustc-env=GIT_HEAD={head}");
     tauri_build::build()
 }

     heartwood,
     nix-playwright-browsers,
     ...
   }@inputs:
   }:
     (flake-utils.lib.eachDefaultSystem (system: let
       pkgs = import nixpkgs {
         inherit system;

           nix-playwright-browsers.overlays.${system}.default
         ];
       };
       inherit (pkgs) lib;
     in {
       checks = {

               PLAYWRIGHT_SKIP_BROWSER_DOWNLOAD = 1;
               PLAYWRIGHT_SKIP_VALIDATE_HOST_REQUIREMENTS = true;
               RUST_SRC_PATH = "${rTc}/lib/rustlib/src/rust/library";
             };
             } // (
               if self ? rev || self ? dirtyRev
               then {
                 GIT_HEAD = self.rev or self.dirtyRev;
               }
               else {}
             );
             preCheck = ''
               export RAD_HOME="$PWD/_rad-home"