fix(legacy): declare GetTransactionRpcResult's meta as nullable

[joncinque]

Problem

As reported in https://solana.stackexchange.com/questions/7981/structerror-at-path-meta-expected-an-object-but-received-null-gettransac, when calling getTransaction directly, the deserialization of the response fails because there's no meta field, and GetTransactionRpcResult requires it.

Note that GetParsedTransactionRpcResult correctly declares the meta field as nullable, and the docs say that meta may be null https://docs.solana.com/api/http#gettransaction

Solution

Make GetTransactionRpcResult consistent with its parsed cousin, and declare the meta as nullable

[buffalojoec]

[joncinque]

I don't have write access to the repo -- can you merge it for me?

[github-actions]

🎉 This PR is included in version 1.87.5 🎉

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[github-actions]

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