[BUG]init_actions skips event hooks with underscore-prefixed names since v2.1.0

[tingQian]

Issue Title

[Bug] init_actions skips event hooks with underscore-prefixed names since v2.1.0

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Issue Body

Description

In Beanie 2.1.0, PR #1293 (chore: modernize Beanie codebase and types for py310+) introduced a change in init_actions() that skips all attributes starting with _. This silently breaks any @before_event / @after_event hooks whose method names begin with an underscore.

Location

beanie/odm/utils/init.py, method init_actions:

for attr in dir(cls):
    if attr.startswith("_"):  # Skip all private/magic attributes  <-- THIS LINE
        continue

Reproduction

from beanie import Document, before_event, Insert

class MyDocument(Document):
    name: str
    creator_id: str | None = None

    @before_event(Insert)
    async def _set_creator(self):
        """This hook is silently skipped in 2.1.0!"""
        self.creator_id = "some_user"

# After init_beanie(...) and calling:
doc = MyDocument(name="test")
await doc.insert()
print(doc.creator_id)  # None in 2.1.0, "some_user" in 2.0.0

Beanie 2.0.0: _set_creator is correctly registered and fires on insert. ✅
Beanie 2.1.0: _set_creator is skipped by init_actions because it starts with _, and creator_id remains None. ❌

Expected Behavior

Hooks decorated with @before_event / @after_event should be registered regardless of whether the method name starts with _. The has_action attribute check is already sufficient to filter relevant methods.

Actual Behavior

All methods starting with _ are silently skipped during action registration, even if they are valid user-defined hooks with @before_event / @after_event decorators. No error or warning is raised.

Impact

• Silent data loss: No error, no warning — hooks simply stop executing.
• Breaking change: Not documented in any changelog or migration guide.
• Users who followed a naming convention like _before_create / _after_update for hooks are affected.
• In our case, this caused creator_id and updater_id fields to silently become null in production after upgrading from 2.0.0 to 2.1.0.

Suggested Fix

Instead of skipping all _-prefixed attributes, only skip dunder attributes:

for attr in dir(cls):
    if attr.startswith("__"):  # Skip only dunder/magic attributes
        continue

Or, even better, keep the optimization but still check has_action for _-prefixed methods:

for attr in dir(cls):
    if attr.startswith("__"):  # Skip magic/dunder attributes (performance optimization)
        continue
    f = getattr(cls, attr)
    if inspect.isfunction(f) and hasattr(f, "has_action"):
        ActionRegistry.add_action(
            document_class=cls,
            event_types=f.event_types,
            action_direction=f.action_direction,
            funct=f,
        )

This preserves the performance optimization (skipping __init__, __repr__, etc.) while not breaking user-defined hooks with single-underscore prefixes.

Environment

• Beanie version: 2.1.0 (works correctly in 2.0.0)
• Python: 3.11
• Introduced in: PR chore: modernize Beanie codebase and types for py310+ #1293, commit 24b2a7bf

Labels suggestion

bug, regression