Python upgrade

[srugano]

PayDunya Python Client — Complete Modernization

Complete modernization of the PayDunya Python client: new packaging, tooling, and full coverage of the officially documented APIs (PAR, PER, DMP, IPN), with Pydantic v2 validation.

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Changes

🏗️ Packaging & Tooling

• Migrated to src/ layout with hatchling build backend (PEP 621)
• Python ≥ 3.10 required; dropped Python 2 legacy
• Replaced requests → httpx, flake8 → ruff, Travis CI → GitHub Actions
• Added uv (lockfile), tox (py310–py313), pre-commit (ruff + standard hooks)
• MkDocs Material documentation site in docs/

✨ New Features

• PaydunyaClient(master_key, private_key, token, mode="test"|"live") — typed, explicit client
• DMP API — DMP.create() / DMP.check_status() for SMS/Email payment requests
• IPN helper — verify_ipn_hash() (SHA-512 master-key comparison)
• Customer pre-fill — Invoice.set_customer(name, email, phone)
• Pydantic v2 models with boundary validation (EmailStr, amount bounds, required fields)

🔧 Docs Compliance Fixes

• Items now serialized as keyed item_0, item_1... (was a flat array starting at item_1)
• Removed OPR class — endpoints no longer exist in official docs (replaced by JS-based PSR flow, now documented in docs/psr.md)

🧪 Testing

• 50 pytest tests, fully mocked via pytest-httpx — no network or credentials needed
• 97% coverage, enforced in tox
• examples/sandbox_e2e.py — interactive sandbox script for manual testing with fictitious customer accounts

💥 Breaking Changes

See CHANGELOG.md:

• v1 global-state API (paydunya.debug / paydunya.api_keys) replaced by PaydunyaClient
• OPR removed