Decode escaped JSON Pointer refs

[kriptoburak]

Summary

• decode escaped JSON Pointer tokens before looking up $defs entries
• keep unresolved refs unchanged when a decoded definition is still missing
• add coverage for slash and tilde escapes in $defs refs

Validation

• npm install from the existing lockfile
• npm test
• npm run typecheck
• npm run build
• npm pack dry run
• npm audit omit dev
• git diff check