fix: return error for malformed program account filters

[jeffhelius]

Problem

• The getProgramAccounts RPC endpoint would silently ignore malformed filters and execute an unfiltered query, potentially causing unnecessary load on the node.

Summary of Changes

• Added error handling to get_spl_token_owner_filter and get_spl_token_mint_filter to return a JSON-RPC error when malformed filters are provided
• This prevents fallback to unfiltered queries which could be resource-intensive
• Improves error visibility for API users

Fixes #

[mergify]

If this PR represents a change to the public RPC API:

1. Make sure it includes a complementary update to rpc-client/ (example)
2. Open a follow-up PR to update the JavaScript client @solana/web3.js (example)

Thank you for keeping the RPC clients in sync with the server API @jeffhelius.