Refactor _hooks.py into organized sibling modules by category

Split the large _hooks.py file (1132 lines) into three focused modules:

- _hook_config.py: Configuration classes and type definitions
  (HookspecOpts, HookimplOpts, HookspecConfiguration, HookimplConfiguration)

- _hook_markers.py: Hook decorators and specifications
  (HookspecMarker, HookimplMarker, HookSpec, varnames utility)

- _hook_callers.py: Hook caller implementations and HookImpl
  (HookCaller protocol, NormalHookCaller, HistoricHookCaller, SubsetHookCaller, HookRelay, HookImpl)

The original _hooks.py now serves as a backward compatibility module that
re-exports all symbols, maintaining 100% API compatibility.

Updated all internal imports across the codebase to use the new module
structure while preserving existing public interfaces.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: RonnyPfannschmidt

src/pluggy/__init__.py

@@ -18,16 +18,16 @@
     "PluggyWarning",
     "PluggyTeardownRaisedWarning",
 ]
-from ._hooks import HistoricHookCaller
-from ._hooks import HookCaller
-from ._hooks import HookImpl
-from ._hooks import HookimplConfiguration
-from ._hooks import HookimplMarker
-from ._hooks import HookimplOpts
-from ._hooks import HookRelay
-from ._hooks import HookspecConfiguration
-from ._hooks import HookspecMarker
-from ._hooks import HookspecOpts
+from ._hook_callers import HistoricHookCaller
+from ._hook_callers import HookCaller
+from ._hook_callers import HookImpl
+from ._hook_callers import HookRelay
+from ._hook_config import HookimplConfiguration
+from ._hook_config import HookimplOpts
+from ._hook_config import HookspecConfiguration
+from ._hook_config import HookspecOpts
+from ._hook_markers import HookimplMarker
+from ._hook_markers import HookspecMarker
 from ._manager import PluginManager
 from ._manager import PluginValidationError
 from ._project import ProjectSpec

src/pluggy/_callers.py

@@ -11,7 +11,7 @@
 from typing import NoReturn
 import warnings
 
-from ._hooks import HookImpl
+from ._hook_callers import HookImpl
 from ._result import HookCallError
 from ._result import Result
 from ._warnings import PluggyTeardownRaisedWarning