fix: correct array concatenation and randomness usage in UintNote

[HusseinAdeiza]

Summary

This PR addresses and corrects Noir compatibility, code safety, and style issues in uint_note.nr.
Improvements include safer randomness usage, robust array concatenation, updated constant declarations, and clarified assertions. These changes ensure the contract logic remains secure, maintainable, and compatible with current Noir standards.

Problem

• The previous code used potentially unsafe randomness and array concatenation that may not be fully supported in Noir.
• Constants were declared using outdated syntax.
• Assertion statements included custom messages, which may not be supported in all Noir versions.
• The code and tests mixed styles that could cause confusion or errors for future maintainers.

Solution

• Replaced unsafe randomness with Noir’s recommended random() usage.
• Refactored array concatenation and padding logic to use idiomatic Noir patterns.
• Updated constants to use const for clarity and compatibility.
• Simplified assertion statements to avoid unsupported custom messages.
• Improved comments and test code for readability and maintainability.

How to Test

1. Run all contract tests:

   noir test -b uint-note

2. Ensure all tests pass and compilation succeeds.
3. Verify the contract logic, especially note creation, partial note handling, and packing/unpacking, works as intended.

Additional Context

These changes align the code with best practices for Noir development and should reduce future technical debt.
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