fix(observability): explicitly initialize LifecycleDispatcher guard attributes

[cofin]

Summary

Fixes AttributeError: 'LifecycleDispatcher' object has no attribute 'has_pool_create' when SQLSpec is installed with mypyc compilation enabled.

The Problem

• LifecycleDispatcher used dynamic __slots__ with tuple unpacking (*GUARD_ATTRS)
• When compiled with mypyc, getattr() calls on dynamically created slot attributes failed
• This caused crashes when using non-pooling adapters (ADBC, BigQuery) with mypyc builds
• Error only manifested in production builds with HATCH_BUILD_HOOKS_ENABLE=1

The Solution

Explicitly define and initialize all guard attributes:

__slots__ = (
    "_hooks",
    "_counters",
    "has_pool_create",
    "has_pool_destroy",
    # ... all guard attributes listed explicitly
)

def __init__(self, hooks):
    # Initialize all guards to False first
    self.has_pool_create = False
    self.has_pool_destroy = False
    # ... then set correct values via setattr()

Key Features

• All guard attributes explicitly listed in __slots__ (no tuple unpacking)
• All attributes initialized to False before dynamic assignment
• Maintains backward compatibility with existing code
• No performance impact on runtime behavior

Testing

• Added test test_lifecycle_dispatcher_guard_attributes_always_accessible()
• Validates all guard attributes accessible even with no hooks
• Tested with ADBC and BigQuery (non-pooling adapters)
• All existing observability tests pass