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