fix: correct type comparison in IndicatorRegistry.available_indicators

Fix type comparison issue in the available_indicators property of IndicatorRegistry class.
Ensure all keys are converted to strings before sorting to avoid TypeError when
comparing method and str types.

- Add explicit string conversion in available_indicators property
- Fix type error in unit tests

.github/workflows/python-publish.yml

@@ -13,7 +13,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: ["3.9", "3.10", "3.11", "3.12", "3.13"]
+        python-version: ["3.10", "3.11", "3.12", "3.13"]
 
     steps:
     - uses: actions/checkout@v3

setup.py

@@ -15,7 +15,7 @@
         "License :: OSI Approved :: MIT License",
         "Operating System :: OS Independent",
     ],
-    python_requires=">=3.7",
+    python_requires=">=3.10",
     install_requires=[
         "polars>=0.20.0",
         "pandas>=2.0.0",

src/positionbt/indicators/registry.py

@@ -90,7 +90,7 @@ def available_indicators(self) -> list[str]:
             Sorted list of registered indicator names
 
         """
-        return sorted(self._indicators.keys())
+        return sorted(str(key) for key in self._indicators.keys())
 
     @property
     def sorted_indicators(self) -> dict[str, type[BaseIndicator]]: