WordLoom implementation extensions: file_bindings

[uogbuji]

pylib/ext/file_includes.py: extension module. Has resolve_file_bindings() and internal helpers for file:, dir:, and glob: reference resolution, with directory-traversal protection, size/encoding guards, and hidden-path filtering. Adapted and cleaned up from the scratch prototype.

pylib/wordloom.py:

• language_item gains a file_bindings: dict attribute (empty by default) and a render(**kwargs) method that merges file_bindings with runtime kwargs before formatting. clone() also preserves file_bindings.
• load() gains features= (set or dict; {'file-inclusion'} enables the extension) and base_dir= (explicit override). It auto-detects the loom base directory from Path arguments, path strings, and open() handles. The extension import is deferred inside load() so the extension is only loaded when the feature is active.

test/test_file_inclusion.py: 16 tests covering file:, dir: & glob: resolution, all three input forms (Path, open handle, path string), render() merging, security rejections (path traversal, absolute paths, missing files, .. in globs), base_dir= override & clone() propagation.

implementation.md: developer-facing doc covering package layout, language_item attributes and methods, the full load() parameter reference, and a detailed section on the file-inclusion extension including TOML syntax, the three schemes, security model, and the base-directory requirement.