Replace explicit match + panics in const contexts with const-`expect()`

[nbdd0121]

Previously, we use explicit match + panics inside const contexts because expect() is not const-stable, e.g. the c_str! macro. It was stabilised in Rust 1.83, so we can switch to use it.

This would require change of makefiles to enable the feature globally, or wait until we bump our MSRV.

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[ojeda]

or wait until we bump our MSRV.

Unless something happens, I will bump it this cycle, so we could put this one on top.

[nbdd0121]

I'll lower this from medium to easy when the MSRV bump happens.