fix: :bug: Components CPI caller check

[iamnamananand996]

Status	Type	⚠️ Core Change	Issue
Ready	Bug	Yes	#29

Problem

• Components make use of solana_program::sysvar::instructions::get_instruction_relative to enforce that they are called from CPI and the identify of the caller, This may contains a bug, since a transaction could contain a valid instruction at index [0], but be malicious.

Full description is available: https://github.com/magicblock-labs/bolt/issues/29#issuecomment-2408909957

Solution

To correctly determine if your program was called via CPI, you should:

• Use get_instruction_relative(-1, ...): This will attempt to retrieve the instruction that called the currently executing instruction. If the program was called directly, there will be no instruction at index -1, and the function will return an error.

• Check for Errors: If get_instruction_relative(-1, ...) returns an Err, it means the program was called directly. If it returns Ok, you can proceed, knowing it was called via CPI.

cc - @GabrielePicco