add python lock files

Author: molpopgen

python/requirements.txt

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+tskit>=0.6.3
+pytest

python/requirements_locked_3_13.txt

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+# This file was autogenerated by uv via the following command:
+#    uv pip compile -p 3.13 requirements.txt
+attrs==25.3.0
+    # via
+    #   jsonschema
+    #   referencing
+iniconfig==2.1.0
+    # via pytest
+jsonschema==4.23.0
+    # via tskit
+jsonschema-specifications==2025.4.1
+    # via jsonschema
+numpy==2.2.5
+    # via tskit
+packaging==25.0
+    # via pytest
+pluggy==1.6.0
+    # via pytest
+pytest==8.3.5
+    # via -r requirements.txt
+referencing==0.36.2
+    # via
+    #   jsonschema
+    #   jsonschema-specifications
+rpds-py==0.25.0
+    # via
+    #   jsonschema
+    #   referencing
+tskit==0.6.3
+    # via -r requirements.txt