Refactor package name from 'mata' to 'datamata' in all files

[bimantoromaesa]

What

Rename PyPI distribution from mata to datamata. The Python import name (import mata) is unchanged — this follows the PIL/Pillow precedent where users pip install datamata but write import mata in code.

Changes across 5 phases:

• pyproject.toml — name = "datamata"; self-referencing all and dev extras updated to datamata[...]
• .github/workflows/publish.yml — switched to OIDC Trusted Publisher auth (id-token: write + environment: pypi); trigger on push: tags: ["v*"] unchanged
• 14 runtime ImportError hints across 10 source files — pip install mata[...] → pip install datamata[...]
• 4 test assertions in test_ocr_adapter.py (×3) and test_valkey_exporter.py (×1) — synced to new hint strings
• Docs & examples — all pip install mata install instructions updated across README.md, QUICKSTART.md, CHANGELOG.md, 8 example scripts, examples/graph/scenarios/README.md, and 6 files under docs/

Why

The package name mata is unavailable on PyPI. Distributing as datamata unblocks the v1.9.2 release while keeping zero breaking changes for existing users (import mata stays identical).

Checklist

• Tests pass (pytest tests/ -v) — 4517 passed, 11 skipped, 0 failures
• Linters pass (black --check src/ tests/ && ruff check src/)
• Type checks pass (mypy src/mata/)
• Documentation updated (if user-facing changes)
• CHANGELOG.md updated (if notable change)