fix: Don't panic on out-of-range integer literals in const positions

[shulaoda]

Writing an array length that doesn't fit in usize, like [u8; 18446744073709551616], makes rust-analyzer panic and then spam the log with Propagating panic for cycle head ... over and over.

The problem is in intern_const_ref: it interns the literal with ScalarInt::try_from_uint(..).unwrap(), but try_from_* returns None when the value doesn't fit the target type, so the unwrap() blows up inside a salsa query. I changed those three integer branches (and usize_const) to return an error const instead of unwrapping, so an out-of-range literal is just treated as an error rather than crashing.

Also added a regression test. Running analysis-stats on the repro reports panics: 1 before the change and panics: 0 after.

Closes #22620

[Veykril]

Thanks!

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