fix: only run unit tests during Nix build, skip integration tests

Changed from selectively skipping test modules to running only --lib
tests (unit tests). This is cleaner and more maintainable.

Integration tests (tests/*.rs) require:
- git binary in PATH
- Ability to spawn subprocesses
- Network access for some tests
- TestRelay fixture (spawns ngit-grasp)

These requirements don't work in the Nix sandbox, so we run only
unit tests (--lib) during package build. Full integration test suite
runs in environments where git is available:
- Local dev (nix develop includes git)
- CI/CD (git installed)
- Manual testing (cargo test runs all tests)

flake.nix

@@ -50,17 +50,11 @@
 
           buildInputs = with pkgs; [ openssl ];
 
-          # Skip tests that require git in PATH (sandboxing issue)
-          # These tests run fine in dev environment and CI
-          checkFlags = [
-            # Unit tests that spawn git subprocesses
-            "--skip=git::subprocess::tests::"
-            "--skip=git::tests::"
-            "--skip=purgatory::helpers::tests::"
-            # Integration tests that create git repos
-            "--skip=common::git_server::"
-            "--skip=common::purgatory_helpers::"
-          ];
+          # Skip all integration tests during Nix build (require git in PATH)
+          # Integration tests run in dev environment and CI where git is available
+          doCheck = true;
+          cargoTestFlags =
+            [ "--lib" ]; # Only run unit tests, skip integration tests
         };
       })) // {
         # NixOS module for deployment

nix/module.nix

@@ -18,17 +18,10 @@ let
     nativeBuildInputs = with pkgs; [ pkg-config ];
     buildInputs = with pkgs; [ openssl ];
 
-    # Skip tests that require git in PATH (sandboxing issue)
-    # These tests run fine in dev environment and CI
-    checkFlags = [
-      # Unit tests that spawn git subprocesses
-      "--skip=git::subprocess::tests::"
-      "--skip=git::tests::"
-      "--skip=purgatory::helpers::tests::"
-      # Integration tests that create git repos
-      "--skip=common::git_server::"
-      "--skip=common::purgatory_helpers::"
-    ];
+    # Skip all integration tests during Nix build (require git in PATH)
+    # Integration tests run in dev environment and CI where git is available
+    doCheck = true;
+    cargoTestFlags = [ "--lib" ]; # Only run unit tests, skip integration tests
   };
 
   # Per-instance options