Add generated test label files to .gitignore

The generate_label_test in diskann-providers writes output files to the
cwd using relative paths. Ignore the resulting rand_labels_50_10K_*.txt
files so they don't get accidentally committed.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: JordanMaples

.gitignore

@@ -336,4 +336,7 @@ target/
 .history/
 
 # Ignore local settings for claude code AI agent
-.claude/settings.local.json
+.claude/settings.local.json
+
+# Generated test data from generate_synthetic_labels tests
+rand_labels_50_10K_*.txt