Implement DiscordGateway503Filter for logging

[Twilights-0]

Added a logging filter to handle Discord Gateway 503 errors.

[Copilot]

Pull request overview

Adds a targeted logging filter to suppress noisy Discord gateway “503 Service Unavailable” handshake warnings and replace them with a single cleaner warning emitted by the application logger.

Changes:

• Introduces DiscordGateway503Filter to detect Discord gateway 503 handshake failures and rewrite the log output.
• Registers the filter on the discord.client logger during main() startup.

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[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

Suppressed comments (1)

src/fablabot/main.py:58

• Logging a new message from inside a logging filter adds side effects and can lead to confusing ordering or re-entrancy issues. Since the goal is just to de-noise this specific 503 warning, it’s safer to rewrite the existing record (and clear exc_info) and let the original logger emit it, rather than emitting a second log and returning False.

            logger.warning(
                "Discord Gateway indisponible (503). %s",
                retry_message,
            )