ens-referrals: move referrer encode/decode to ens-referrals

[shrugs]

spec via #1908 (comment)

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[coderabbitai]

🔗 Related PRs

#1553 - Add getDefaultEnsNodeUrl [merged]
#1575 - fix: add correct ensv1 and ensv2 addresses to sepolia-v2 namespace [merged]
#1586 - fix: update ENSv1Registry address in ens-test-env devnet config [merged]
#1758 - fix: allow ensv2 apis to be used without ensv2 datasource [merged]
#1858 - Remove nodejs version info from data model [merged]

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