feat: Implement HEIC/HEIF parsing and rebuilding utilities

- Add `heic_types.py` to define structures for HEIC/HEIF boxes including ItemLocationBox, ItemInfoEntryBox, and others.
- Introduce parsing logic in `parser.py` to handle various box types and their contents, including nested structures.
- Implement rebuilding functionality for ItemLocationBox to adjust offsets based on new metadata.
- Enhance ItemInfoBox to correctly parse and build content for ItemInfoEntry.
- Update `pyproject.toml` to include project metadata and dependencies.

README.md

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+# pyheic-struct
+
+Utilities for inspecting, modifying, and rebuilding HEIC/HEIF files with a focus on
+cross-vendor quirks between Samsung and Apple motion photos.
+
+## Features
+
+- Lightweight parser that exposes core ISOBMFF boxes (`ftyp`, `meta`, `iloc`, `iinf`, etc.)
+- Helpers for reconstructing Samsung grid images into flat HEIC pictures
+- Rebuilder that writes updated metadata and payload offsets safely
+- High-level `convert_samsung_motion_photo` function to create Apple-compatible
+  HEIC/MOV pairs (with optional MOV ContentIdentifier injection via `exiftool`)
+- CLI tool: `pyheic-struct samsung.heic`
+
+## Installation
+
+```bash
+pip install .
+```
+
+## Usage
+
+```python
+from pyheic_struct import convert_samsung_motion_photo
+
+convert_samsung_motion_photo("samsung.heic")
+```
+
+Command line:
+
+```bash
+pyheic-struct samsung.heic --output-heic samsung_fixed.HEIC
+```
+
+## Development
+
+The package targets Python 3.10+. Run the CLI in editable mode:
+
+```bash
+python -m pyheic_struct path/to/samsung.heic
+```