[test] BlockHeightMiddleware

[kien6034]

Problem definition
Related issues: #13

Commit changes:
8f92d8d

Testing
The test should verify that the BlockHeightMiddleware correctly:

• Parses the height query parameter
• Sets the GRPCBlockHeightHeader appropriately
• Handles error cases properly

Acceptance criteria
Specificy the desired outcomes of resolving this issue.

• Valid height parameters are correctly propagated to the GRPCBlockHeightHeader
• Invalid height formats return appropriate syntax errors
• Negative heights are properly rejected
• Zero height queries are handled correctly
• Empty height parameter allows the request to pass through unchanged