Fix no_std panic in Byte::from_f64/from_f32 on non-finite input

[dualfroz]

Problem

Byte::from_f64 and Byte::from_f32 are documented to return None when the
input is "too large" or not >= 0. In std builds a non-finite input such as
f64::INFINITY correctly returns None, but in no_std builds it panics:

// with `--no-default-features --features byte`
byte_unit::Byte::from_f64(f64::INFINITY);
// thread panicked at src/common.rs:39:
// called `Option::unwrap()` on a `None` value

So the same call behaves differently across the two build configurations and
breaks the documented contract in no_std.

Root cause

from_f64/from_f32 guard the input with if size >= 0.0, which rejects
NaN (since NaN >= 0.0 is false) but lets +inf through. The value is then
passed to ceil_f64/ceil_f32 in src/common.rs.

The std implementation uses v.ceil(), which returns inf; the subsequent
inf as u128/as u64 cast saturates to the maximum, and the range check then
returns None.

The no_std implementation instead does:

Decimal::from_f64(v).unwrap().ceil().to_f64().unwrap()

Decimal::from_f64 (and from_f32) returns None for non-finite values, so
.unwrap() panics. The no_std helper therefore diverges from the std one.

Fix

Make the no_std ceil_f64/ceil_f32 fall back to the input value when it is
not representable as a Decimal (i.e. non-finite), mirroring f64::ceil:

match Decimal::from_f64(v) {
    Some(d) => d.ceil().to_f64().unwrap_or(v),
    None => v,
}

With this, from_f64(f64::INFINITY) flows through the same saturating cast and
range check as in std, returning None. Finite values are unaffected.

Test

Added from_non_finite_returns_none to tests/byte.rs, asserting that
from_f64/from_f32 return None for both infinity and NaN. It passes under
--all-features and under --no-default-features --features byte (the config
that previously panicked).