Add LEXam evaluation results

Adds LEXam (Benchmarking Legal Reasoning on 340 Law Exams) evaluation results from the official leaderboard at https://lexam-benchmark.github.io/.

See https://huggingface.co/datasets/LEXam-Benchmark/LEXam for the benchmark and https://arxiv.org/abs/2505.12864 for the paper.

.eval_results/lexam.yaml

@@ -0,0 +1,14 @@
+- dataset:
+    id: LEXam-Benchmark/LEXam
+    task_id: open_question
+  value: 14.88
+  source:
+    url: https://lexam-benchmark.github.io/
+    name: LEXam Leaderboard
+- dataset:
+    id: LEXam-Benchmark/LEXam
+    task_id: mcq_4_choices
+  value: 26.27
+  source:
+    url: https://lexam-benchmark.github.io/
+    name: LEXam Leaderboard