Issue Type: Bug / Code Correctness

[chymak0vadina]

Issue Type: Bug / Code Correctness

Title: Fix missing error handling for unsupported network parameter in CdpClient.evm.sendTransaction

Description:
In the TypeScript CDP SDK (@coinbase/cdp-sdk), calling cdp.evm.sendTransaction({ …, network }) with an unsupported or mistyped network string (e.g., "ethereum" instead of "base-sepolia" or "base") currently results in a generic error or failed RPC call without a clear SDK-level validation. This can lead to cryptic errors during runtime and make it hard for developers to diagnose issues related to network configuration. :contentReference[oaicite:0]{index=0}

Expected behavior:

• If an unsupported or invalid network string is passed into cdp.evm.sendTransaction (or related EVM methods), the SDK should validate the network parameter early.
• The method should throw a clear and descriptive error (e.g., Unsupported network: ${network}) before attempting any RPC or API call.
• The error message should list valid supported networks for quick reference.

Proposed solution:

• Add validation logic in the core EVM client wrapper before making API or RPC calls.
• Use a centralized list of supported networks (e.g., from the SDK’s configuration or a const enum).
• Update types so that network ideally accepts only a union of valid network identifiers where possible.
• Add unit tests verifying that invalid network values throw with clear messages.

Acceptance criteria:

• Passing an invalid network to sendTransaction, requestFaucet, createAccount, etc., throws a descriptive SDK error.
• Tests are added to cover incorrect network parameter usage.
• No breaking behavior for existing valid network calls.