Add improper_instruction_introspection lint

[S3v3ru5]

The lint checks for this issue in building-secure-contracts: https://github.com/crytic/building-secure-contracts/tree/master/not-so-smart-contracts/solana/improper_instruction_introspection

The lint is very trivial, it flags all calls to load_instruction_at_checked(...).

[S3v3ru5]

This lint needs further work.

The lint might not work and should be considered incomplete. It was not possible to compile the lint, hence not tested, ran (Could not run even clippy on the lint). This is the error:

error[E0658]: use of unstable library feature 'offset_of'
   --> /Users/vara/.cargo/registry/src/index.crates.io-6f17d22bba15001f/solana-program-1.18.1/src/program.rs:542:20
    |
542 |         assert_eq!(offset_of!(AccountInfo, executable), 42);
    |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: see issue #106655 <https://github.com/rust-lang/rust/issues/106655> for more information
    = help: add `#![feature(offset_of)]` to the crate attributes to enable
    = note: this error originates in the macro `_memoffset__offset_of_impl` which comes from the expansion of the macro `offset_of` (in Nightly builds, run with -Z macro-backtrace for more info)

Latest version of solana-program 1.18.7 gives the same error. I could not resolve the error.

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