fix: remove ref length validation

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.03 :warning:

Comparison is base (edd0de9) 88.34% compared to head (5a1a679) 88.31%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #57 +/- ## ========================================== - Coverage 88.34% 88.31% -0.03% ========================================== Files 19 19 Lines 7446 7445 -1 ========================================== - Hits 6578 6575 -3 - Misses 868 870 +2 ``` | [Impacted Files](https://codecov.io/gh/bihealth/hgvs-rs/pull/57?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=bihealth) | Coverage Δ | | |---|---|---| | [src/parser/impl\_validate.rs](https://codecov.io/gh/bihealth/hgvs-rs/pull/57?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=bihealth#diff-c3JjL3BhcnNlci9pbXBsX3ZhbGlkYXRlLnJz) | `84.44% <100.00%> (-0.67%)` | :arrow_down: | ... and [2 files with indirect coverage changes](https://codecov.io/gh/bihealth/hgvs-rs/pull/57/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=bihealth) 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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