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

.editorconfig

@@ -0,0 +1,24 @@
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true
+indent_style = space
+indent_size = 4
+
+[*.{c,h,cu}]
+indent_size = 4
+
+[*.{ts,tsx,js,json,css}]
+indent_size = 2
+
+[Makefile]
+indent_style = tab
+
+[*.yml]
+indent_size = 2
+
+[*.md]
+trim_trailing_whitespace = false