Incorrect size estimate for base64 decode buffer for BinaryView

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Describe the bug

The upper bound of the output buffer size for binary view is estimated using its memory buffer size.

datafusion/datafusion/functions/src/encoding/inner.rs

Line 297 in 050046a

encoding.decode_array::<_, i32>(&array, array.get_buffer_memory_size())

This is incorrect as it can underestimate required memory when the BinaryView contains significant duplication and views point to overlapping regions in the buffers.

base64 decode will fail with Output slice too small due to this bad estimate.

To Reproduce

The following test case could trigger this bug

datafusion/datafusion/functions/src/encoding/inner.rs

    #[test]
    fn test_estimate_view_size() {
        let mut builder = BinaryViewBuilder::new().with_deduplicate_strings();
        for _ in 0..1000 {
            builder.append_value([65u8; 64]);
        }
        let arr = ArrayBuilder::finish(&mut builder);
        println!("{}", arr.get_buffer_memory_size());
        Encoding::Base64Padded
            .decode_array::<_, i32>(&arr.as_binary_view(), arr.get_buffer_memory_size())
            .unwrap();
    }

Expected behavior

No response

Additional context

This bug might have a much larger blast radius.

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take