fix: correct executable compile docs to match signatures and flow

[MozirDmitriy]

This change corrects misleading and outdated Rustdoc in cairo-lang-executable/src/compile.rs. The prepare_db() docs incorrectly stated it compiles a function by path and now accurately describe building a RootDatabase configured for #[executable], including cfg flags, plugin suite, corelib detection, and unsafe_panic handling. The compile_executable_function_in_prepared_db() docs previously listed a non-existent diagnostics_reporter parameter and claimed an Ok(Vec) return type; they now reflect the actual signature, the returned CompileExecutableResult<'db>, and clarify that diagnostics are ensured by the caller via ensure_diagnostics in compile_executable_in_prepared_db(). These updates align the documentation with the code and with the established pattern used in the Starknet compile module, removing ambiguity for users and maintainers.

[reviewable-StarkWare]

This change is 

[orizi]

Reviewable status: 0 of 1 files reviewed, 1 unresolved discussion

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crates/cairo-lang-executable/src/compile.rs line 206 at r1 (raw file):

///
/// Returns a ready-to-use database for subsequent compilation steps.
pub fn prepare_db(config: &ExecutableConfig) -> Result<RootDatabase> {

you added a function here - why?