fix(sdk): critical bug fixes, adapter standardisation, test revival & full documentation rewrite

[Einswilli]

Description

This PR addresses the major gaps identified in the EasySwitch SDK codebase — from critical runtime bugs to incomplete provider implementations and outdated documentation. 38 commits, 46 tests passing.

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Critical Fixes (Phase 1)

• Provider enum: Added missing providers (Paystack, MTN, Airtel Money, QosPay, PayPlus, KkiaPay, PayDunya) and 10 missing currencies (UGX, TZS, KES, etc.)
• Semoa adapter: Complete rewrite — was broken due to all() misuse (passed multiple args instead of iterable), private _validate_credentials (abstract method not implemented), sync/async mismatch, missing @register() decorator, cancel_transaction returning super().send_payment() nonsense
• MTN adapter: Complete rewrite — was using legacy Config class, incompatible send_payment signature (kwargs instead of TransactionDetail), treating HTTPResponse objects as raw dicts, no registry registration
• Paystack validate_webhook: Signature was incompatible with BaseAdapter (accepted raw_body: bytes instead of payload: Dict)
• Bizao webhooks: validate_webhook/parse_webhook were delegating to abstract super() — guaranteed TypeError at runtime
• Empty stubs: QosPay, PayPlus, KkiaPay, PayDunya, adapters/interfaces.py — all 0-byte files replaced with proper implementations or removed

Standardisation (Phase 2)

• All adapters now use async with self.get_client() as client: consistently
• response.status_code → response.status throughout (PayGate, Semoa)
• All validate_webhook implementations return bool (not raise AuthenticationError)
• Added **kwargs to EasySwitchError base so UnsupportedOperationError(provider=...) works everywhere
• Normalised HTTPResponse.data access (removed dead hasattr(response, "json") branches)

Core Infrastructure (Phase 3)

• Removed legacy Config dataclass (was unused, replaced by Pydantic RootConfig)
• Fixed EnvConfigSource — lowercase provider keys and double-underscore _X_ prefix causing config validation failures
• Activated MAX_AMOUNT validation in BaseAdapter.validate_transaction
• Fixed validate_webhook_signature in validators (used repr() instead of json.dumps() — non-deterministic)
• Fixed phone number validation (double-zero prefix case like 00228...)
• Fixed RateLimitError passing unsupported headers= kwarg
• Added environment/timeout back to RootConfig as top-level globals

Tests (Phase 4)

• Zero → 46 passing tests across all 4 test files
• Fixed all mock patterns to properly patch get_client() with async context managers
• Fixed all assertions to use Provider/TransactionStatus enums instead of raw strings
• Fixed config fixtures to match RootConfig schema (uppercase provider keys, no extra fields)
• Fixed asyncio.run() conflict in async test context

Documentation (Phase 5)

• Full guides for CinetPay, Semoa, Bizao (were just # Under development)
• New guides for Paystack, MTN MoMo, Airtel Money
• Provider Feature Matrix — operations, currencies, flows, rate limits across all 8 providers
• Rewritten home page with provider ecosystem grid
• Updated all API reference pages to match current code signatures and enums
• Fixed FedaPay examples (was using asyncio.run() inline — bad practice)
• Fixed PayGate guide (wrong env var names, missing webhooks section)
• Updated mkdocs.yml navigation with all providers
• Normalised .env.sample with all providers and fixed EVIRONMENT typos

[Wgoeh]

Great thanks!