Refactored Kate RPC module to remove code duplication across query_rows, query_proof, and query_multiproof methods.

[letmehateu]

Pull Request type

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• Feature
• Bugfix
• Refactor
• Format
• Documentation
• Testing
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Description

This PR refactors the Kate RPC module to eliminate code duplication across query methods.

Problem:
Three methods (query_rows, query_proof, query_multiproof) contained duplicated validation and conversion logic:

• Commitment validation was duplicated 3 times (18 lines)
• Cell limit validation was duplicated 2 times (18 lines)
• Cell-to-position conversion was duplicated 2 times (8 lines)

Solution:
Extracted common logic into three helper methods:

• ensure_has_commitments() - validates that block has non-empty commitments
• validate_cells_limit() - checks that requested cell count doesn't exceed configured limit
• cells_to_positions() - converts Cells to position tuples (row, col)

Impact:

• Removed 40 lines of duplicated code
• Added 30 lines of reusable helper methods
• Net reduction: 10 lines
• Improved maintainability and reduced risk of inconsistent updates
• No behavioral changes - pure refactoring

Related Issues

N/A

Testing Performed

• Code reviewed for correctness
• Verified no linter errors with cargo clippy
• Confirmed behavioral equivalence - all methods maintain same logic flow
• Validated that helper methods correctly encapsulate the extracted logic

Checklist

• I have performed a self-review of my own code.
• The tests pass successfully with cargo test.
• The code was formatted with cargo fmt.
• The code compiles with no new warnings with cargo build --release and cargo build --release --features runtime-benchmarks.
• The code has no new warnings when using cargo clippy.
• If this change affects documented features or needs new documentation, I have created a PR with a documentation update.

[letmehateu]

@jakubcech hello, can you check please my PR?