Add Buildkite CI pipeline

- Add .buildkite/pipeline.yml with build/test matrix for Ruby 3.2, 3.3, 3.4
- Include Rust installation for native extension compilation
- Add RuboCop lint step
- Update minimum Ruby version to 3.2.0

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: catkins

.buildkite/pipeline.yml

@@ -0,0 +1,27 @@
+steps:
+  - group: ":ruby: Build & Test"
+    steps:
+      - label: ":ruby: Ruby {{matrix.ruby}}"
+        command:
+          - curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y
+          - source ~/.cargo/env
+          - bundle install
+          - bundle exec rake compile
+          - bundle exec rake spec
+        image: "ruby:{{matrix.ruby}}"
+        matrix:
+          setup:
+            ruby:
+              - "3.2"
+              - "3.3"
+              - "3.4"
+        env:
+          BUNDLE_PATH: vendor/bundle
+
+  - label: ":rubocop: Lint"
+    command:
+      - bundle install
+      - bundle exec rubocop
+    image: "ruby:3.4"
+    env:
+      BUNDLE_PATH: vendor/bundle

slatedb.gemspec

@@ -12,7 +12,7 @@ Gem::Specification.new do |spec|
   spec.description = "A cloud-native embedded key-value store built on object storage"
   spec.homepage = "https://github.com/catkins/slatedb-rb"
   spec.license = "Apache-2.0"
-  spec.required_ruby_version = ">= 3.1.0"
+  spec.required_ruby_version = ">= 3.2.0"
 
   spec.metadata["homepage_uri"] = spec.homepage
   spec.metadata["source_code_uri"] = "https://github.com/catkins/slatedb-rb"