Removes default bert scorer init (#234)
* move init of bertscorer to avoid downloading model by default
* Update src/lighteval/metrics/metrics_sample.py
Co-authored-by: Nathan Habib <30601243+NathanHB@users.noreply.github.com>
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Co-authored-by: Nathan Habib <30601243+NathanHB@users.noreply.github.com>
