fix: replace mutable default arguments in Config methods

[AaryanCode69]

Summary

Replace mutable default arguments ({} and []) with None in two Config methods to prevent potential shared-state issues across calls.

In Python, default argument values are evaluated once at function definition time, meaning mutable defaults can be shared between calls if mutated.
Reference: https://docs.python.org/3/faq/programming.html#why-are-default-values-shared-between-objects

---

Problem

Two methods in src/util/config_yml/__init__.py use mutable default arguments:

# Line ~40
def get_messages(self, ..., last_messages: dict[str, str] = {})

# Line ~57
def get_message_rate_usage_limited(self, ..., message_times_queue: list[str] = [])

If these objects are ever mutated in-place (e.g., dict[key] = value or list.append()), the mutation persists across subsequent calls, which may lead to unintended shared state.

This pattern is commonly flagged by Python linters:

• pylint → W0102
• flake8-bugbear → B006
• ruff → B006

---

Solution

Use None as the default value and instantiate a fresh object inside the function body.

def get_messages(
    self,
    user_id: str | None = None,
    event: TriggerEvent | None = None,
    after_messages: int | None = None,
-   last_messages: dict[str, str] = {},
+   last_messages: dict[str, str] | None = None,
) -> dict[str, str]:

+   if last_messages is None:
+       last_messages = {}

def get_message_rate_usage_limited(
    self,
    user_id: str | None = None,
-   message_times_queue: list[str] = [],
+   message_times_queue: list[str] | None = None,
) -> MessageRate | None:

+   if message_times_queue is None:
+       message_times_queue = []

---

Impact

• No behavioral change for current callers.
• Prevents potential shared mutable state if the default arguments are used in future code paths.
• Aligns with common Python best practices and linter recommendations.

---

Files Changed

• src/util/config_yml/__init__.py

Fixes #130