v0.18.8 of sip_cli

Manage mono-repos with `sip`, run scripts and get dependencies concurrently. Changelog excerpt: ## Enhancements - **Experimental, opt-in:**Add `--experimental-bucket`to `sip test`for Flutter packages, combining test files into ~CPU-core-count generated bucket files (dispatched as one `flutter test`invocation per shard) to cut per-file VM-isolate startup overhead, the same idea as the existing Dart-only test optimizer. Files that can't be safely combined (unsafe `TestWidgetsFlutterBinding`subtypes, or test-surface mutation without a reset) always run in their own isolated wrapper, never sh[...]