fix: resolve CI failures across all workflows

aitbc-agent-sdk (package-tests.yml):
- Add AITBCAgent convenience class matching test expectations
- Fix test_agent_sdk.py: was importing nonexistent AITBCAgent, now tests
  the real API (Agent.create, AgentCapabilities, to_dict) plus AITBCAgent
- Fix 3 remaining mypy errors: supported_models Optional coercion (line 64),
  missing return types on _submit_to_marketplace/_update_marketplace_offer
- Run black on all 5 src files — zero mypy errors, zero black warnings
- All 6 tests pass

python-tests.yml:
- Add pynacl to pip install (aitbc-crypto and aitbc-sdk import nacl)
- Add pynacl>=1.5.0 to root requirements.txt

Service readiness (api-endpoint-tests.yml, integration-tests.yml):
- Replace curl -sf with curl http_code check — -sf fails on 404 responses
  but port 8006 (blockchain RPC) returns 404 on / while being healthy
- Blockchain RPC uses REST /rpc/* endpoints, not JSON-RPC POST to /
  Fix test_api_endpoints.py to test /health, /rpc/head, /rpc/info, /rpc/supply
- Remove dead test_rpc() function, add blockchain RPC to perf tests
- All 4 services now pass: coordinator, exchange, wallet, blockchain_rpc
- Integration-tests: check is-active before systemctl start to avoid
  spurious warnings for already-running services

Hardhat compile (smart-contract-tests.yml, package-tests.yml):
- Relax engines field from >=24.14.0 to >=18.0.0 (CI has v24.13.0)
- Remove 2>/dev/null from hardhat compile/test so errors are visible
- Remove 2>/dev/null from npm run build/test in package-tests JS section

packages/py/aitbc-agent-sdk/src/aitbc_agent/compute_consumer.py

@@ -15,6 +15,7 @@ logger = logging.getLogger(__name__)
 @dataclass
 class JobRequest:
     """Compute job request specification"""
+
     consumer_id: str
     job_type: str
     model_id: Optional[str] = None
@@ -28,6 +29,7 @@ class JobRequest:
 @dataclass
 class JobResult:
     """Result from a compute job"""
+
     job_id: str
     provider_id: str
     status: str  # "completed", "failed", "timeout"
@@ -46,9 +48,13 @@ class ComputeConsumer(Agent):
         self.completed_jobs: List[JobResult] = []
         self.total_spent: float = 0.0
 
-    async def submit_job(self, job_type: str, input_data: Dict[str, Any],
-                         requirements: Optional[Dict[str, Any]] = None,
-                         max_price: float = 0.0) -> str:
+    async def submit_job(
+        self,
+        job_type: str,
+        input_data: Dict[str, Any],
+        requirements: Optional[Dict[str, Any]] = None,
+        max_price: float = 0.0,
+    ) -> str:
         """Submit a compute job to the network"""
         job = JobRequest(
             consumer_id=self.identity.id,