fix: Improve floating point lint to handle ambiguous type

[odysa]

Fixes: #14897, #10015

This is not a perfect solution, but it fixes the issue. Happy to discuss further with the clippy team.

This PR refines check_mul_add to avoid false positives on ambiguous float types (e.g., f32 vs f64). It improves type detection and ensures mul_add is only suggested when the type is clear.

Changes:

• Improved detection of ambiguous float types
• Refined mul_add suggestion logic
• Added tests for ambiguous cases

Example

Before this change, expressions like:

let x = 1.0; // ambiguous type
let _ = x * 2.0 + 0.5; // could incorrectly suggest mul_add

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changelog: [suboptimal_flops]: improve handling of ambiguous float types in mul_add suggestions

[rustbot]

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[llogiq]

I agree that a suboptimal solution is better than no solution.

[llogiq]

Thanks, and we can do a followup PR if we happen upon a better solution.