ci: refactor Gitea workflows to use environment variables for workspace paths

- Added WORKSPACE env variable to all workflow jobs
- Changed hardcoded workspace paths to use ${{ env.WORKSPACE }}
- Added pull_request path filters to blockchain-sync-verification.yml
- Updated cross-chain-tests.yml path filters to apps/blockchain-node/** and scripts/multi-node/**
- Removed ait-devnet from default chains in cross-chain-tests.yml
- Disabled test-cross-chain-bridge job (test file not implemented)
- Removed test-cross-chain-bridge from aggregate

apps/blockchain-node/src/aitbc_chain/cross_chain.py

@@ -18,7 +18,7 @@ class CrossChainSync:
             self.sync_status[chain] = {
                 "synced": True,
                 "height": 0,
-                "last_sync": datetime.now(UTC).isoformat(),
+                "last_sync": datetime.now(timezone.utc).isoformat(),
             }
 
 
@@ -36,5 +36,5 @@ class MultiChainConsensus:
                 "consensus_reached": True,
                 "height": 0,
                 "validators": 1,
-                "last_consensus": datetime.now(UTC).isoformat(),
+                "last_consensus": datetime.now(timezone.utc).isoformat(),
             }