rfl::Generic: Allow int64_t -> double conversion in to_double

[Curve]

See #548.

This PR allows implicit conversion of int64_t values stored in rfl::Generic to double (via to_double) if no loss of precision occurs.

[gemini-code-assist]

Summary of Changes

Hello @Curve, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the rfl::Generic utility by extending the functionality of its to_double() method. Previously, this method strictly required the underlying value to be a double. Now, it intelligently handles int64_t values, allowing them to be converted to double only when such a conversion guarantees no loss of precision, thereby improving flexibility while maintaining data integrity.

Highlights

• int64_t to double Conversion: The rfl::Generic::to_double() method now supports converting int64_t values to double.
• Precision Safeguard: This conversion is only performed if it can be done without any loss of precision. If precision would be lost, an rfl::Error is returned instead of the converted value.

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[gemini-code-assist]

Code Review

This pull request correctly implements a feature to allow converting int64_t values stored in rfl::Generic to double, including a check to prevent loss of precision. The logic for the conversion is sound. However, I've identified a critical issue where the new error-handling path can throw an exception inside a noexcept-qualified function. This would lead to program termination. My review includes a comment detailing this issue and how to resolve it by removing the noexcept specifier from to_double() and other similar functions in the class.

[liuzicheng1987]

@Curve , thanks for your contribution!

[Curve]

@Curve , thanks for your contribution!

No problem, thanks for the quick merge!