[Variant] Offer `simdutf8` as an optional dependency when validating metadata

[friendlymatthew]

This is a follow up on #7878

The variant spec states the string values in the metadata dictionary must be UTF-8 encoded strings.

We do this check here:

arrow-rs/parquet-variant/src/variant/metadata.rs

Lines 250 to 252 in 387490a

	// Verify the string values in the dictionary are UTF-8 encoded strings.
	let value_buffer =
	string_from_slice(self.bytes, 0, self.first_value_byte as _..self.bytes.len())?;

Since we offer simdutf8 as an optional dependency in other crates, we could do the same when performing the validation above. See @Dandandan's comment.

The rough idea being:

If simdutf8 is supported, do:

let value_str = simdutf8::basic::from_utf8(value_buffer)?;

else, default to the existing implementation

[friendlymatthew]

@alamb this seems like a good first issue

[codephage2020]

take

[alamb]

FWIW I think given @Dandandan 's comment it would also be fine to simply always use simdutf8 too

Thank you @codephage2020 and @friendlymatthew

[friendlymatthew]

FWIW I think given @Dandandan 's comment it would also be fine to simply always use simdutf8 too

Oh, for some reason I understood the comment as use simdutf8 as an optional dependency like the parquet crate

[Dandandan]

FWIW I think given @Dandandan 's comment it would also be fine to simply always use simdutf8 too

Oh, for some reason I understood the comment as use simdutf8 as an optional dependency like the parquet crate

Yeah I think there was a reason to make this optional (WASM maybe?).

[alamb]

Makes sense -- thank yu

[alamb]

label_issue.py automatically added labels {'parquet'} from #7908