Improve Base62 encoding/decoding performance and robustness

[redouan-rhazouani]

Describe your changes

Performance & Robustness Enhancements

• Optimize Base62 decoding by replacing strings.IndexRune with a fixed-size array for O(1) lookups, reducing memory overhead.
• Reduce heap allocations and improve Base62.Encode performance by avoiding dynamic memory usage for small, fixed-size data.
• Use iterative multiplication instead of math.Pow() to avoid floating-point precision issues.
• Add an overflow check when calculating the decoded value to prevent silent overflow of uint32, ensuring correctness for long input strings.

Testing Improvements:

• Enhance unit tests by explicitly verifying encoding and decoding accuracy.
• Add unit tests for Base62 decoding: one for overflow handling and another for empty strings.
• Add a unit test for input strings containing invalid characters.

Issue ticket number and link

Checklist

• Is it a bug fix
• Is a typo/documentation fix
• Is a feature enhancement
• It is a refactor
• Created tests that fail without the change (if possible)
• Extended the README / documentation, if necessary

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All committers have signed the CLA.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

Pull Request Overview

This PR improves Base62 encoding and decoding performance while enhancing robustness and error handling. Key changes include:

• Optimized encoding by using a fixed-size buffer and iterative multiplication.
• Improved decoding with a fixed-size lookup array, added overflow and invalid character checks.
• Expanded unit tests to cover edge cases including empty input, overflow, and invalid characters.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
base62/base62.go	Refactored encoding/decoding logic for performance and robustness.
base62/base62_test.go	Added comprehensive tests for encoding/decoding, error handling.