Resolve clippy type_complexity warnings in geophysical config prompts

[Copilot]

Clippy flagged the return types of prompt_gravity_config() and prompt_magnetic_config() as excessively complex: Option<(GeoResolution, Option<f64>, Option<f64>, Option<String>)>.

Changes

• Added GeoMeasurementConfig type alias to represent the tuple structure
• Updated function signatures to use the new type alias
• Documented each tuple field (resolution, bias, noise std dev, map file path)

/// Type alias for geophysical measurement configuration returned by prompt functions.
///
/// Contains:
/// - `GeoResolution`: The map resolution to use
/// - `Option<f64>`: Measurement bias (mGal for gravity, nT for magnetic)
/// - `Option<f64>`: Measurement noise standard deviation
/// - `Option<String>`: Map file path (auto-detected if None)
type GeoMeasurementConfig = (
    strapdown::sim::GeoResolution,
    Option<f64>,
    Option<f64>,
    Option<String>,
);

fn prompt_gravity_config() -> Option<GeoMeasurementConfig> { /* ... */ }
fn prompt_magnetic_config() -> Option<GeoMeasurementConfig> { /* ... */ }

The type alias is a zero-cost abstraction that preserves existing tuple destructuring patterns in calling code.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Simplify the geophysical config propmting functions.</issue_title>
<issue_description>Clippy lint gives the following suggestions:

warning: very complex type used. Consider factoring parts into `type` definitions
    --> sim/src/main.rs:1460:31
     |
1460 |   fn prompt_gravity_config() -> Option<(
     |  _______________________________^
1461 | |     strapdown::sim::GeoResolution,
1462 | |     Option<f64>,
1463 | |     Option<f64>,
1464 | |     Option<String>,
1465 | | )> {
     | |__^
     |
     = help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.91.0/index.html#type_complexity
     = note: `#[warn(clippy::type_complexity)]` on by default

warning: very complex type used. Consider factoring parts into `type` definitions
    --> sim/src/main.rs:1526:32
     |
1526 |   fn prompt_magnetic_config() -> Option<(
     |  ________________________________^
1527 | |     strapdown::sim::GeoResolution,
1528 | |     Option<f64>,
1529 | |     Option<f64>,
1530 | |     Option<String>,
1531 | | )> {
     | |__^
     |
     = help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.91.0/index.html#type_complexity

Please address these suggestions to improve code readability and maintainability.

Instructions:

• Only modify the following files: sim/src/main.rs; sim/src/common.rs; core/src/sim.rs. If your plan should involve changes to other files, please explain why in the issue body.

Acceptence criteria:

• The clippy warnings about complex types in sim/src/main.rs should be resolved.
• The code should remain functionally equivalent after the changes.
• The changes should be well-documented with comments explaining the new type definitions.
• All tests should pass successfully after the modifications.

Comments on the Issue (you are @copilot in this section)

• Fixes Simplify the geophysical config propmting functions. #218

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[Copilot]

Pull request overview

This PR resolves clippy type_complexity warnings by introducing a type alias for complex tuple return types in geophysical configuration prompt functions.

• Adds GeoMeasurementConfig type alias to simplify function signatures
• Updates prompt_gravity_config() and prompt_magnetic_config() to use the new type alias
• Includes comprehensive documentation explaining each tuple field