Fix base encoding edge cases

[baixiangcpp]

Summary

• fix Base58 all-zero byte encoding/decoding so leading zero bytes round trip without an extra zero
• tighten Base32 decode validation for impossible lengths, malformed padding, and non-zero trailing bits
• add regression tests for the audited edge cases

TDD evidence

• New tests failed first against the existing implementation:
  • encodeBytesToBase58([0]) returned "11" instead of "1"
  • malformed Base32 inputs such as "A", "AAA", "MZ======", and "MZXW6YTBOI=" were accepted

Verification

• npm test -- tests/unit/base-encoding-utils.test.ts
• npm test -- tests/unit/base-encoding-utils.test.ts tests/unit/yaml-json-converter-utils.test.ts
• npm run lint
• npm run validate
• npm test
• git diff --check

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