feat: implement incremental sync (#1)

- Add incremental image sync to avoid re-transferring unchanged layers
- Migrate logging from custom macros to tracing crate
- Refactor error types: split AppError into ConfigError + DomainError
- Add constants module for markers, logs, and directory names
- Add StageType and SchedulerType enums (replacing string literals)
- Modularize repx-executor into context, runtime/, error, util modules
- Extract test harness into repx-test-utils crate
- Add smart sync tests and data-only local target tests
- Clean up nix files and update flake.locks

Author: hakan-demirli

.github/workflows/main.yml

@@ -34,8 +34,14 @@ jobs:
       fail-fast: false
       matrix:
         check:
-          - repx-rs-tests
           - repx-py-tests
+          - rs-client-tests
+          - rs-unit
+          - rs-bwrap
+          - rs-gc
+          - rs-integration
+          - rs-containers
+          - rs-executor
           - integration
           - invalidation
           - pipeline_logic
@@ -57,6 +63,7 @@ jobs:
           - e2e-mount-paths-podman
           - e2e-impure-docker
           - e2e-mount-paths-docker
+          - incremental-sync
     steps:
       - uses: actions/checkout@v4
       - uses: DeterminateSystems/nix-installer-action@v11