fix(api): validate HTTP status code in Solana RPC GetTotalSupply

[Tyagiquamar]

In \�pi/internal/rpc.go, \GetTotalSupply\ previously passed non-200 HTTP responses (e.g., HTTP 429 rate limit or 503 gateway error) directly to \json.NewDecoder(resp.Body).Decode(&rpcResp). This resulted in obscure JSON decoding error messages ('EOF' or 'invalid character') rather than identifying the upstream RPC HTTP status failure.

This fix:

1. Validates that
   esp.StatusCode == http.StatusOK\ before attempting JSON deserialization and returns a clear status error otherwise.
2. Adds unit test coverage (\TestSolanaClient_GetTotalSupply_HTTPError) in \�pi/internal/server_test.go.

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[Tyagiquamar]

Hi, friendly ping for review on this PR when you have a moment. Happy to address any feedback. Thanks!