Allow derived enum keys

[ChiragAgg5k]

Summary

• preserve the existing empty x-enum-keys convention for derived identifiers
• continue rejecting partial non-empty mappings

Tests

• composer check

[greptile-apps]

Greptile Summary

This PR allows an explicitly empty x-enum-keys list to retain the existing derived-identifier convention while continuing to reject partial non-empty mappings.

• Exempts empty enum-key lists from enum-length validation.
• Adds focused coverage for explicit empty lists and derived names.

Confidence Score: 5/5

The PR appears safe to merge with no actionable correctness or security issues identified.

The parser consistently represents absent and explicitly empty enum-key mappings as an empty list, while the unchanged non-empty cardinality validation continues to reject partial mappings.

Important Files Changed

Filename	Overview
src/Parser/Schema/Reader.php	The enum-key validation now accepts an empty list while preserving cardinality checks for non-empty mappings; no actionable defect was identified.
tests/Schema/ReaderTest.php	Adds focused regression coverage confirming that an explicit empty mapping remains represented as derived enum keys.

_{Reviews (1): Last reviewed commit: "fix: allow derived enum keys" | Re-trigger Greptile}