database: Test heed get_range

[gzalz]

What

Test the get_range function in storage/database/src/backend/heed/database.rs.

Why

This is meant to address issue #348 .

Where

This is related to the heed database backend and related tests.

How

This PR is meant to address a perceived misunderstanding in issue #348 . The table insertions in the test have incrementing keys but all have a value equal to 0u64.

get_range is defined to return Values rather than Keys, as per the function signature, yet in the reproduction code all the Values must equal 0.

impl<T: Table> DatabaseIter<T> for HeedTableRo<'_, T> {
    #[inline]
    fn get_range<'a, Range>(
        &'a self,
        range: Range,
    ) -> Result<impl Iterator<Item = Result<T::Value, RuntimeError>> + 'a, RuntimeError>
    where
        Range: RangeBounds<T::Key> + 'a

If we wish to test get_range we should be checking the Values within the new loop, as this is what get_range returns. I believe the functionality of get_range is correct.