packaging: pyproject.toml + editorconfig + clang-format

Python packaging:
- pyproject.toml: pip install colibri-engine (editable dev install works)
- colibri/ package with __version__, CLI entry point delegating to c/coli
- Optional dependency groups: [convert] (numpy, huggingface_hub),
  [oracle] (torch, transformers, safetensors), [bench] (tokenizers, datasets)

Code style:
- .editorconfig: consistent indent/charset across all file types
- .clang-format: LLVM-based, 120 col, matches existing engine style

Usage:
  pip install -e .              # dev install (CLI + serve, no heavy deps)
  pip install -e .[convert]     # adds converter dependencies
  pip install -e .[oracle]      # adds torch/transformers for oracle validation

.clang-format

@@ -0,0 +1,10 @@
+BasedOnStyle: LLVM
+IndentWidth: 4
+ColumnLimit: 120
+AllowShortFunctionsOnASingleLine: All
+AllowShortIfStatementsOnASingleLine: AllIfsAndElse
+AllowShortLoopsOnASingleLine: true
+BreakBeforeBraces: Attach
+PointerAlignment: Right
+SpaceAfterCStyleCast: false
+SortIncludes: false