add max borrow withdraw query

[ashleychandy]

Description

Adds a no-op instruction to query the maximum amount a marginfi account can borrow or withdraw from a given bank without reproducing the on-chain risk engine off-chain.

The instruction simulates borrow/withdraw operations using the existing risk checks and emits the result as an event, making it easy to consume via RPC simulation.

Changes

• Add lending_account_query_max_borrow_withdraw instruction
• Add QueryMaxBorrowWithdrawEvent for RPC simulation output
• Implement binary search to determine the maximum borrow amount
• Implement binary search to determine the maximum withdraw amount
• Return is_all when the entire user balance can be withdrawn
• Reuse existing borrow/withdraw logic and health checks without mutating state
• Export the new instruction through the program entrypoint

Fixes #627