Refactor chainId from number to string in contractSubscriptions

[d4mr]

PR-Codex overview

This PR focuses on changing the data type of the chainId field in the contract_subscriptions table from Int to String. It updates related code to ensure consistent handling of chainId as a string.

Detailed summary

• Altered chainId column type in the contract_subscriptions table to TEXT.
• Updated createContractSubscription.ts to convert chainId to a string.
• Changed schema.prisma to reflect chainId as a String.
• Modified contractSubscription.ts to parse chainId as an integer.
• Adjusted getContractSubscriptions.ts to convert chainId to a string in queries.
• Updated the return value in getContractSubscriptionsUniqueChainIds to parse chainId as an integer.

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