Organize evaluation and metric artifacts

#1
astraq-vl-stage2-full-heldout-eval-v1.zip → evaluations/full-heldout/astraq-vl-stage2-full-heldout-eval-v1.zip RENAMED
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phase0_stage2_results.zip → evaluations/phase0/phase0_stage2_results.zip RENAMED
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astraq-vl-stage2-metrics.zip → metrics/astraq-vl-stage2-metrics.zip RENAMED
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eval_loss_curve.png → metrics/eval-loss-curve/eval_loss_curve.png RENAMED
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eval_loss_curve.zip → metrics/eval-loss-curve/eval_loss_curve.zip RENAMED
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