fix(tests): fix variable shadowing, untested invalid inputs, and array length mismatch in c32encoding tests

[jadonamite]

What does this PR do?

Fixes three bugs in the c32encoding test suite and adds inline comments for maintainability.

Changes

• Fix variable shadowing: renamed .map() callback parameter from testData to entry in c32encodingRandomBytes to avoid shadowing the outer array
• Fix silently skipped assertions: split grouped try/catch blocks in c32checkEncode invalid inputs into individual blocks so every invalid case is independently tested
• Fix array length mismatch: removed extra trailing undefined from hexMinLengths (had 23 elements for 22 hex strings)

Testing

All existing tests pass. No new tests added — fixes ensure existing invalid input tests actually run as intended.