feat(solana-client-tools): add program zero-copy account fetch helper

[vihu]

Summary

Closes malbeclabs/doublezero#3877

Add a shared solana-client-tools helper for fetching all zero-copy accounts of a given type from a program via getProgramAccounts.

Changes

• Added try_fetch_program_zero_copy_accounts<T> as both:
  • a SolanaConnection method
  • a free helper accepting &RpcClient
• Builds a getProgramAccounts request with:
  • discriminator memcmp filter at offset 0
  • Base64 account encoding
  • caller-supplied commitment
• Skips zero-lamport/closed accounts before deserialization.
• Deserializes remaining accounts through ZeroCopyAccountOwnedData<T>.
• Returns contextual errors for malformed non-zero accounts, including pubkey and target type.
• Added unit coverage for RPC config construction, closed-account skipping, and malformed-account errors.
• Added direct solana-account-decoder-client-types dependency for account encoding.