refactor: modernise RPM builder with Python tooling v2

- Migrate from legacy shell-based build system to modern Python tooling
- Update all metadata.yaml files to new schema with per-distro builds
- Standardise build scripts with curl -L, envsubst, and error handling
- Convert nfpm.yaml templates to use environment variable substitution
- Update Dockerfile to accept all package metadata as build arguments
- Modernise Makefile to use new Python build tool commands
- Update CI workflow to use tools/build instead of make

rpms/ruff/metadata.yaml

@@ -1,9 +1,18 @@
-name: ruff
-release: 6
-version: 0.8.1
-build:
-- distro: el/8
-  image: git.unkin.net/unkin/almalinux8-rpmbuilder:latest
-- distro: el/9
-  image: git.unkin.net/unkin/almalinux9-rpmbuilder:latest
+---
+arch: amd64
+builds:
+  - image: git.unkin.net/unkin/almalinux8-rpmbuilder:latest
+    release: '6'
+    repository: [almalinux/el8]
+    version: 0.8.1
+  - image: git.unkin.net/unkin/almalinux9-rpmbuilder:latest
+    release: '6'
+    repository: [almalinux/el9]
+    version: 0.8.1
+description: An extremely fast Python linter and code formatter, written in Rust.
 github: astral-sh/ruff
+homepage: https://docs.astral.sh/ruff/
+license: Apache-2.0
+maintainer: Astral.sh
+name: ruff
+platform: linux