Use less precision when comparing vaue in slint language

In rust, use f32 instead of f64 for arithmetic comparison.
In the interpreter, use approx_eq

The test is failling in nightly because of precision change in `log`.
By using f32, it actually should work

Also Revert "Disable builds with nightly Rust temporarily"
This reverts commit 4afc3a2e84.

Fixes #5722

internal/compiler/generator/rust.rs

@@ -2184,7 +2184,7 @@ fn compile_expression(expr: &Expression, ctx: &EvaluationContext) -> TokenStream
                             | Type::Rem
                     ) =>
                 {
-                    (Some(quote!(as f64)), Some(quote!(as f64)))
+                    (Some(quote!(as f32)), Some(quote!(as f32)))
                 }
                 _ => (None, None),
             };