`rinex`: increase code coverage

Generate a meaningful library code coverage report with

```bash
cargo tarpaulin --workspace --all-features \
  -t 300 -e rinex-cli -e crx2rnx -e rnx2crx -e ublox-rnx
```

- `--all-features` to cover the entire library
- `--workspace -e $pkg`: exclude applications
- `-t 300s` the default 60s limitation is easily exceeded by our tests

Current code coverage is about __65%__ to this day.