dt.total_nanoseconds and dt.total_microseconds may overflow silently

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Checks

• I have checked that this issue has not already been reported.
• I have confirmed this bug exists on the latest version of Polars.

Reproducible example

from datetime import timedelta
import polars as pl

s = pl.Series([timedelta(days=106752)])
print(s.dt.total_nanoseconds())

Log output

shape: (1,)
Series: '' [i64]
[
        -9223371273709551616
]

Issue description

The Series has time unit us. Getting the total number of nanoseconds requires multiplying the underlying integer by 1000, which may overflow.

We currently use unchecked multiplication for this, while we would need to use checked multiplication and set any overflowing values to null. The fix would be to implement checked arithmetic kernels and use these here.

The offending code is here:

polars/crates/polars-time/src/chunkedarray/duration.rs

Lines 100 to 108 in eb7f939

	/// Extract the nanoseconds from a `Duration`
	fn nanoseconds(&self) -> Int64Chunked {
	match self.time_unit() {
	TimeUnit::Milliseconds => &self.0 * NANOSECONDS_IN_MILLISECOND,
	TimeUnit::Microseconds => &self.0 * 1000,
	TimeUnit::Nanoseconds => self.0.clone(),
	}
	}
	}

Expected behavior

Output should be null rather than wrapping.

Installed versions

main