test: mock test of RPC (#1405)

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<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

- **New Features**
	- Introduced new mock generation capabilities for testing.

- **Bug Fixes**
- Improved mock behavior to handle unspecified return values more
robustly.

- **Tests**
- Expanded test coverage with new cases for subscription queries and
REST endpoint behaviors.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: Ganesha Upadhyaya <ganeshrvce@gmail.com>
Co-authored-by: Ganesha Upadhyaya <gupadhyaya@Ganeshas-MacBook-Pro-2.local>

Author: 3 people

Makefile

@@ -78,6 +78,14 @@ proto-gen:
 	./proto/gen.sh
 .PHONY: proto-gen
 
+## mock-gen: generate mocks of external (commetbft) types
+mock-gen:
+	@echo "-> Generating mocks"
+	mockery --output test/mocks --srcpkg github.com/cometbft/cometbft/rpc/client --name Client
+	mockery --output test/mocks --srcpkg github.com/cometbft/cometbft/abci/types --name Application
+.PHONY: mock-gen
+
+
 ## proto-lint: Lint protobuf files. Requires docker.
 proto-lint:
 	@echo "--> Linting Protobuf files"