Create packaged Git exec aliases for helper commands

- Create a runtime git-exec directory containing git-* aliases that point at the packaged libgit.so binary.
- Set GIT_EXEC_PATH for every native Git invocation so Git subcommands like fetch, merge-base, upload-pack, and receive-pack resolve the same way in tests and on-device.
- Keep JVM tests on GitRepositoryRuntime with the compiled host libgit.so so Push exercises the packaged-runtime execution model.

app/build.gradle.kts

@@ -19,8 +19,8 @@ android {
         applicationId = "solutions.tretter.githugandroid"
         minSdk = 26
         targetSdk = 35
-        versionCode = 123
-        versionName = "0.1.122"
+        versionCode = 124
+        versionName = "0.1.123"
 
         testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
         vectorDrawables.useSupportLibrary = true