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/codegen/cnodes.py

@@ -0,0 +1,156 @@
+"""
+AST nodes specific to the C family of languages
+"""
+
+from sympy.codegen.ast import (
+    Attribute, Declaration, Node, String, Token, Type, none,
+    FunctionCall, CodeBlock
+    )
+from sympy.core.basic import Basic
+from sympy.core.containers import Tuple
+from sympy.core.sympify import sympify
+
+void = Type('void')
+
+restrict = Attribute('restrict')  # guarantees no pointer aliasing
+volatile = Attribute('volatile')
+static = Attribute('static')
+
+
+def alignof(arg):
+    """ Generate of FunctionCall instance for calling 'alignof' """
+    return FunctionCall('alignof', [String(arg) if isinstance(arg, str) else arg])
+
+
+def sizeof(arg):
+    """ Generate of FunctionCall instance for calling 'sizeof'
+
+    Examples
+    ========
+
+    >>> from sympy.codegen.ast import real
+    >>> from sympy.codegen.cnodes import sizeof
+    >>> from sympy import ccode
+    >>> ccode(sizeof(real))
+    'sizeof(double)'
+    """
+    return FunctionCall('sizeof', [String(arg) if isinstance(arg, str) else arg])
+
+
+class CommaOperator(Basic):
+    """ Represents the comma operator in C """
+    def __new__(cls, *args):
+        return Basic.__new__(cls, *[sympify(arg) for arg in args])
+
+
+class Label(Node):
+    """ Label for use with e.g. goto statement.
+
+    Examples
+    ========
+
+    >>> from sympy import ccode, Symbol
+    >>> from sympy.codegen.cnodes import Label, PreIncrement
+    >>> print(ccode(Label('foo')))
+    foo:
+    >>> print(ccode(Label('bar', [PreIncrement(Symbol('a'))])))
+    bar:
+    ++(a);
+
+    """
+    __slots__ = _fields = ('name', 'body')
+    defaults = {'body': none}
+    _construct_name = String
+
+    @classmethod
+    def _construct_body(cls, itr):
+        if isinstance(itr, CodeBlock):
+            return itr
+        else:
+            return CodeBlock(*itr)
+
+
+class goto(Token):
+    """ Represents goto in C """
+    __slots__ = _fields = ('label',)
+    _construct_label = Label
+
+
+class PreDecrement(Basic):
+    """ Represents the pre-decrement operator
+
+    Examples
+    ========
+
+    >>> from sympy.abc import x
+    >>> from sympy.codegen.cnodes import PreDecrement
+    >>> from sympy import ccode
+    >>> ccode(PreDecrement(x))
+    '--(x)'
+
+    """
+    nargs = 1
+
+
+class PostDecrement(Basic):
+    """ Represents the post-decrement operator
+
+    Examples
+    ========
+
+    >>> from sympy.abc import x
+    >>> from sympy.codegen.cnodes import PostDecrement
+    >>> from sympy import ccode
+    >>> ccode(PostDecrement(x))
+    '(x)--'
+
+    """
+    nargs = 1
+
+
+class PreIncrement(Basic):
+    """ Represents the pre-increment operator
+
+    Examples
+    ========
+
+    >>> from sympy.abc import x
+    >>> from sympy.codegen.cnodes import PreIncrement
+    >>> from sympy import ccode
+    >>> ccode(PreIncrement(x))
+    '++(x)'
+
+    """
+    nargs = 1
+
+
+class PostIncrement(Basic):
+    """ Represents the post-increment operator
+
+    Examples
+    ========
+
+    >>> from sympy.abc import x
+    >>> from sympy.codegen.cnodes import PostIncrement
+    >>> from sympy import ccode
+    >>> ccode(PostIncrement(x))
+    '(x)++'
+
+    """
+    nargs = 1
+
+
+class struct(Node):
+    """ Represents a struct in C """
+    __slots__ = _fields = ('name', 'declarations')
+    defaults = {'name': none}
+    _construct_name = String
+
+    @classmethod
+    def _construct_declarations(cls, args):
+        return Tuple(*[Declaration(arg) for arg in args])
+
+
+class union(struct):
+    """ Represents a union in C """
+    __slots__ = ()