[BUG] Fix version import fallback for Python <3.8 compatibility

Replaced direct version import with a fallback mechanism using `importlib.metadata` or `importlib_metadata` for older Python versions. Ensures robust handling of `__version__` even when the package is not properly installed.

Author: Leguark

gempy_engine/__init__.py

@@ -1,3 +1,15 @@
 from gempy_engine.API.model.model_api import compute_model
+from datetime import datetime
 
-from ._version import __version__
+try:
+    from importlib.metadata import version, PackageNotFoundError
+except ImportError:  # For Python <3.8, fallback
+    from importlib_metadata import version, PackageNotFoundError
+
+try:
+    __version__ = version("gempy_engine")  # Use package name
+except ImportError:
+    # If it was not installed, then we don't know the version. We could throw a
+    # warning here, but this case *should* be rare. subsurface should be
+    # installed properly!
+    __version__ = 'unknown-'+datetime.today().strftime('%Y%m%d')