chore: 添加虚拟环境到仓库

- 添加 backend_service/venv 虚拟环境
- 包含所有Python依赖包
- 注意：虚拟环境约393MB，包含12655个文件

backend_service/venv/lib/python3.13/site-packages/sympy/matrices/utilities.py

@@ -0,0 +1,72 @@
+from contextlib import contextmanager
+from threading import local
+
+from sympy.core.function import expand_mul
+
+
+class DotProdSimpState(local):
+    def __init__(self):
+        self.state = None
+
+_dotprodsimp_state = DotProdSimpState()
+
+@contextmanager
+def dotprodsimp(x):
+    old = _dotprodsimp_state.state
+
+    try:
+        _dotprodsimp_state.state = x
+        yield
+    finally:
+        _dotprodsimp_state.state = old
+
+
+def _dotprodsimp(expr, withsimp=False):
+    """Wrapper for simplify.dotprodsimp to avoid circular imports."""
+    from sympy.simplify.simplify import dotprodsimp as dps
+    return dps(expr, withsimp=withsimp)
+
+
+def _get_intermediate_simp(deffunc=lambda x: x, offfunc=lambda x: x,
+        onfunc=_dotprodsimp, dotprodsimp=None):
+    """Support function for controlling intermediate simplification. Returns a
+    simplification function according to the global setting of dotprodsimp
+    operation.
+
+    ``deffunc``     - Function to be used by default.
+    ``offfunc``     - Function to be used if dotprodsimp has been turned off.
+    ``onfunc``      - Function to be used if dotprodsimp has been turned on.
+    ``dotprodsimp`` - True, False or None. Will be overridden by global
+                      _dotprodsimp_state.state if that is not None.
+    """
+
+    if dotprodsimp is False or _dotprodsimp_state.state is False:
+        return offfunc
+    if dotprodsimp is True or _dotprodsimp_state.state is True:
+        return onfunc
+
+    return deffunc # None, None
+
+
+def _get_intermediate_simp_bool(default=False, dotprodsimp=None):
+    """Same as ``_get_intermediate_simp`` but returns bools instead of functions
+    by default."""
+
+    return _get_intermediate_simp(default, False, True, dotprodsimp)
+
+
+def _iszero(x):
+    """Returns True if x is zero."""
+    return getattr(x, 'is_zero', None)
+
+
+def _is_zero_after_expand_mul(x):
+    """Tests by expand_mul only, suitable for polynomials and rational
+    functions."""
+    return expand_mul(x) == 0
+
+
+def _simplify(expr):
+    """ Wrapper to avoid circular imports. """
+    from sympy.simplify.simplify import simplify
+    return simplify(expr)