Add accession to sequence type mapping

[jsstevenson]

A while back, this method got added to VRS-Python to help with HGVS translation:

def extract_sequence_type(alias: str) -> str | None:
    """Provide a convenient way to extract the sequence type from an accession by matching its prefix to a known set of prefixes.

    Args:
    alias (str): The accession string.

    Returns:
    str or None: The sequence type associated with the accession string, or None if no matching prefix is found.

    """
    prefix_dict = {
        "refseq:NM_": "c",
        "refseq:NC_012920": "m",
        "refseq:NG_": "g",
        "refseq:NC_00": "g",
        "refseq:NW_": "g",
        "refseq:NT_": "g",
        "refseq:NR_": "n",
        "refseq:NP_": "p",
        "refseq:XM_": "c",
        "refseq:XR_": "n",
        "refseq:XP_": "p",
        "GRCh": "g",
    }

    for prefix, seq_type in prefix_dict.items():
        if alias.startswith(prefix):
            return seq_type
    return None

I don't really know the context or whether something here already fulfills this need, but it struck me as a bioutils-esque task and I figured I'd throw out the idea of moving it here.