Fixed enum selector bounds checks to prevent validation bypass and JSON panic(issue #6787 )

[mateeaaaaaaa]

Summary

This PR fixes enum selector validation and conversion paths that could mis-handle large unsigned values after signed conversion.

Specifically, it addresses issue #6787 by:

• fixing enum validation to use unsigned bounds checks,
• fixing JSON enum conversion to avoid negative index panic,
• hardening JSUP enum decode to reject negative and out-of-range indexes.

Closes #6787.

What Changed

• value.go
  • Updated enum selector bounds check in checkEnum to compare uint64 values directly.
• sio/jsonio/writer.go
  • Updated convertEnum to avoid int conversion before indexing and safely return "" for invalid selectors.
• sio/jsupio/reader.go
  • Added explicit validation in decodeEnum for:
    • negative indexes,
    • out-of-range indexes.

Tests Added

• value_test.go
  • Added regression test ensuring Validate rejects enum selector math.MaxUint64.
• sio/jsonio/writer_test.go
  • Added regression test ensuring out-of-range enum selector does not panic during JSON write and renders "".
• sio/jsupio/reader_test.go
  • Added tests ensuring JSUP enum decode rejects negative and out-of-range indexes.

Verification

Commands run:

• go test .
• go test ./sio/jsonio ./sio/jsupio

Results:

• All tests passed.

Risk / Compatibility

• Low risk: changes are localized to enum selector validation and conversion paths.
• No API surface changes.
• Behavior for malformed enum selectors is now safe and explicit (error or "") instead of panic/acceptance.