Add sentinel modules for mypyc compilation testing

- Add graphql._sentinel (interpreted fallback)
- Add graphql_mypyc._sentinel (compiled version)
- Include benchmark functions: fibonacci, sum_squares
- SENTINEL_VALUE differentiates compiled vs interpreted

Author: claude

src/graphql/_sentinel.py

@@ -0,0 +1,36 @@
+"""Sentinel module for mypyc compilation testing (interpreted version).
+
+This is the interpreted fallback version. When graphql_mypyc is installed
+and the import hook is active, this module is replaced with the compiled version.
+"""
+
+from __future__ import annotations
+
+__all__ = ["SENTINEL_VALUE", "add_numbers", "fibonacci", "is_compiled", "sum_squares"]
+
+SENTINEL_VALUE: str = "interpreted"
+
+
+def is_compiled() -> bool:
+    """Return True if this module was compiled with mypyc."""
+    return False
+
+
+def add_numbers(a: int, b: int) -> int:
+    """Simple function to test mypyc compilation."""
+    return a + b
+
+
+def fibonacci(n: int) -> int:
+    """Compute fibonacci number recursively."""
+    if n <= 1:
+        return n
+    return fibonacci(n - 1) + fibonacci(n - 2)
+
+
+def sum_squares(n: int) -> int:
+    """Sum of squares from 1 to n."""
+    total = 0
+    for i in range(1, n + 1):
+        total += i * i
+    return total

src/graphql_mypyc/_sentinel.py

@@ -0,0 +1,49 @@
+"""Sentinel module for mypyc compilation testing.
+
+This module is compiled with mypyc to verify the compilation infrastructure
+works correctly. It will be removed once real modules are compiled.
+"""
+
+from __future__ import annotations
+
+__all__ = ["SENTINEL_VALUE", "add_numbers", "fibonacci", "is_compiled", "sum_squares"]
+
+# A constant value that can be checked
+SENTINEL_VALUE: str = "mypyc-compiled"
+
+
+def is_compiled() -> bool:
+    """Return True if this module was compiled with mypyc.
+
+    Checks if the module is loaded from a .so extension file.
+    """
+    return __file__.endswith(".so")
+
+
+def add_numbers(a: int, b: int) -> int:
+    """Simple function to test mypyc compilation.
+
+    This is a simple pure function that benefits from mypyc compilation.
+    """
+    return a + b
+
+
+def fibonacci(n: int) -> int:
+    """Compute fibonacci number recursively.
+
+    This is intentionally slow to show mypyc speedup.
+    """
+    if n <= 1:
+        return n
+    return fibonacci(n - 1) + fibonacci(n - 2)
+
+
+def sum_squares(n: int) -> int:
+    """Sum of squares from 1 to n.
+
+    Loop-based computation that benefits from mypyc.
+    """
+    total = 0
+    for i in range(1, n + 1):
+        total += i * i
+    return total