Fix Duration::from_secs_f32

[manio]

Currently the function is returning wrong values, eg:
Duration::from_secs_f32(30.0);
is giving:
30.000001024s (30s + 1024ns)
This commit fixes this problem.

Fixes: #90225

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @kennytm (or someone else) soon.

Please see the contribution instructions for more information.

[rust-log-analyzer]

The job x86_64-gnu-llvm-12 failed! Check out the build log: (web) (plain)

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

   Compiling unwind v0.0.0 (/checkout/library/unwind)
error[E0308]: mismatched types
   --> library/core/src/time.rs:818:28
    |
818 |         } else if nanos >= MAX_NANOS_F32 {
    |                            ^^^^^^^^^^^^^ expected `f64`, found `f32`
For more information about this error, try `rustc --explain E0308`.
error: could not compile `core` due to previous error
Build completed unsuccessfully in 0:00:08

[manio]

Hmmm... probably bad approach. Closing...