add project tooling and test suite for many-rsync

- Add pyproject.toml: hatchling build, many-rsync entrypoint, ruff/mypy/pytest config
with 60% coverage floor
- Add uv.lock for reproducible dev installs
- Add .pre-commit-config.yaml: ruff (with --fix) + mypy hooks
- Add test_main.py: unit tests for _build_rsync_cmd, _load_raw, and load_config
covering happy paths and FATAL exit cases
- Add explanation.md: architecture overview with flowchart
- main.py: refactor into typed, testable functions (_load_raw, _build_rsync_cmd
extracted); add RsyncParameters/Config TypedDicts; add rsync_parameters config support
(rsync_path, exclude_from); harden validation (n clamped, log_level validated)
- README.md: update install instructions and document all config fields including
rsync_parameters

many-rsync/.pre-commit-config.yaml

@@ -0,0 +1,12 @@
+repos:
+  - repo: https://github.com/astral-sh/ruff-pre-commit
+    rev: v0.15.2
+    hooks:
+      - id: ruff
+        args: [--fix]
+      - id: ruff-format
+
+  - repo: https://github.com/pre-commit/mirrors-mypy
+    rev: v1.19.1
+    hooks:
+      - id: mypy