fix: problem with variants in multi-stop codon txs (#95)

[holtgrewe]

This resolves issues with annotating p.Met1? but also others. See #95 well as biocommons/hgvs#651 for further details.

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (4fccdb8) 88.81% compared to head (3d80d2f) 88.82%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #96 +/- ## ======================================= Coverage 88.81% 88.82% ======================================= Files 19 19 Lines 7983 7989 +6 ======================================= + Hits 7090 7096 +6 Misses 893 893 ``` | [Impacted Files](https://codecov.io/gh/bihealth/hgvs-rs/pull/96?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=bihealth) | Coverage Δ | | |---|---|---| | [src/mapper/altseq.rs](https://codecov.io/gh/bihealth/hgvs-rs/pull/96?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=bihealth#diff-c3JjL21hcHBlci9hbHRzZXEucnM=) | `93.87% <100.00%> (+0.01%)` | :arrow_up: | | [src/mapper/assembly.rs](https://codecov.io/gh/bihealth/hgvs-rs/pull/96?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=bihealth#diff-c3JjL21hcHBlci9hc3NlbWJseS5ycw==) | `80.08% <100.00%> (+0.08%)` | :arrow_up: | | [src/mapper/variant.rs](https://codecov.io/gh/bihealth/hgvs-rs/pull/96?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=bihealth#diff-c3JjL21hcHBlci92YXJpYW50LnJz) | `90.84% <100.00%> (+0.03%)` | :arrow_up: | | [src/normalizer.rs](https://codecov.io/gh/bihealth/hgvs-rs/pull/96?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=bihealth#diff-c3JjL25vcm1hbGl6ZXIucnM=) | `70.79% <100.00%> (+0.02%)` | :arrow_up: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=bihealth). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=bihealth)

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