constexpr for methods of commonly used types

[safocl]

Description

Add constexpr specifier for methods (and constructors) of commonly used types.

Related

Testing

constexpr idf::Frequency f1 = idf::Frequency::Hz(200);
constexpr idf::Frequency f2 = std::clamp(f1, idf::Frequency::Hz(20), idf::Frequency::Hz(2000));

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Checklist

Before submitting a Pull Request, please ensure the following:

• 🚨 This PR does not introduce breaking changes.
• All CI checks (GH Actions) pass.
• Documentation is updated as needed.
• Tests are updated or added as necessary.
• Code is well-commented, especially in complex areas.
• Git history is clean — commits are squashed to the minimum necessary.

[CLAassistant]

All committers have signed the CLA.