Introduce TimestampNs, TimestampTzNs support for Bucket transforms

[sungwy]

Is your feature request related to a problem or challenge?

While working on introducing timestamp_ns and timestamptz_ns support in PyIceberg, I noticed that Bucket transform in iceberg-rust currently doesn't support the transforms for these two types.

Example Error:

FeatureUnsupported => Unsupported data type for bucket transform: Timestamp(Nanosecond, Some("Etc/GMT+10"))

There is currently support for microsecond timestamp, but not for nanoseconds timestamps:

iceberg-rust/crates/iceberg/src/transform/bucket.rs

Lines 160 to 169 in cef87e4

	DataType::Time64(TimeUnit::Microsecond) => input
	.as_any()
	.downcast_ref::<arrow_array::Time64MicrosecondArray>()
	.unwrap()
	.unary(|v| self.bucket_time(v)),
	DataType::Timestamp(TimeUnit::Microsecond, _) => input
	.as_any()
	.downcast_ref::<arrow_array::TimestampMicrosecondArray>()
	.unwrap()
	.unary(|v| self.bucket_timestamp(v)),

Describe the solution you'd like

Bucket transform should successfully be able to transform TimestampNs and TimestampTzNs.

Willingness to contribute

I can contribute to this feature independently