minor code refactor in genome_sequence funcion

[Kaustubh2k5]

Refactor genome_sequence region normalisation

i found this part of the code to be unnecessarily complex (did not see a reason as to why) so i simplified some of the checks without changing any of the code behaviour.

Changes

• Replace type() check with isinstance(region, (list, tuple))
• Replace tuple("*") wildcard comparison with a direct region == "*" check
• Unify single and multi-region paths into a single sequences list
• Rename arrays sequences for clarity
• Make None behaviour explicit (returns all contigs)

Before

genome = self.open_genome()
        if type(region) not in [tuple, list] and region != "*" and region is not None:
            d = self._subset_genome_sequence_region(
                genome=genome,
                region=region,
                inline_array=inline_array,
                chunks=chunks,
            )
        else:
            region = tuple(region)
            if region == tuple("*"):
                region = self.contigs
            d = da.concatenate(
                [
                    self._subset_genome_sequence_region(
                        genome=genome,
                        region=r,
                        inline_array=inline_array,
                        chunks=chunks,
                    )
                    for r in region
                ]
            )
        return d

After

        genome = self.open_genome()

        if region == "*" or region is None:
            regions = self.contigs
        elif isinstance(region, (list, tuple)):
            regions = list(region)
        else:
            regions = [region]

        sequences = [
            self._subset_genome_sequence_region(
                genome=genome,
                region=r,
                inline_array=inline_array,
                chunks=chunks,
            )
            for r in regions
        ]

        if len(sequences) == 1:
            return sequences[0]
        return da.concatenate(sequences)

Issues targeted:

#1171