Determine how to return MANE data with more than one mane_select

[Here](https://github.com/cancervariants/variation-normalization/blob/main/variation/validators/validator.py#L676), we determine which MANE data to return in the response. We are taking the result with the highest count. However, this is not the best approach. If there are two distinct `mane_select` results each with a `count = 1` it will return the first match it found. This is likely the problem of #136 failing occasionally. For some reason, accessions somehow change order when running the same query multiple times.

@MayLiu27 stated that in their database, they know the `c.` position of the transcript they are talking about. Maybe we could provide a parameter giving a known position to help decide in these cases?