Display more descriptive error on missing manifest

Before:

  ```
  ❯ aiken check
  Error:
    × No such file or directory (os error 2)
  ```

  After:

  ```
  ❯ aiken check
  Error:
    × Missing 'aiken.toml' manifest in /Users/ktorz/Documents/Projects/aiken-lang/aiken
    help: Try running `aiken new <REPOSITORY/PROJECT>` to initialise a project with an example manifest.
  ```

  Co-authored-by: KtorZ <matthias.benkort@gmail.com>

crates/cli/src/lib.rs

@@ -1,9 +1,7 @@
-use std::collections::BTreeMap;
-use std::{env, path::PathBuf, process};
-
 use aiken_project::{pretty, script::EvalInfo, telemetry, Project};
 use miette::IntoDiagnostic;
 use owo_colors::OwoColorize;
+use std::{collections::BTreeMap, env, path::PathBuf, process};
 use uplc::machine::cost_model::ExBudget;
 
 pub mod cmd;