Enable const tests for bool methods

[dollaransh17]

This change re-enables the const tests for bool::then_some and bool::then that were previously disabled with a FIXME comment referencing issue 110395.

The tests verify that these methods work correctly in const contexts, which is important for compile-time evaluation. These tests check that both the eager evaluation variant (then_some) and lazy evaluation variant (then) can be used to create constant Option values at compile time.

Tests added:

• Const evaluation of false.then_some(0) returning None
• Const evaluation of true.then_some(0) returning Some(0)
• Const evaluation of false.then(zero) returning None
• Const evaluation of true.then(zero) returning Some(0)

[rustbot]

r? @Mark-Simulacrum

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[rust-log-analyzer]

The job aarch64-gnu-llvm-20-1 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

[RUSTC-TIMING] build_script_build test:false 0.339
error[E0493]: destructor of `T` cannot be evaluated at compile-time
  --> library/core/src/bool.rs:36:37
   |
36 |     pub const fn then_some<T>(self, t: T) -> Option<T> {
   |                                     ^ the destructor for this type cannot be evaluated in constant functions
37 |         if self { Some(t) } else { None }
38 |     }
   |     - value is dropped here

For more information about this error, try `rustc --explain E0493`.
[RUSTC-TIMING] core test:false 24.092