feat: add recurrence rule support to GuildScheduledEvent

[Mantouisyummy]

Summary

This pull request adds support for recurrence rules to GuildScheduledEvent.

• Introduces a new recurrence_rule parameter to Guild.create_scheduled_event and GuildScheduledEvent.
• Adds the GuildScheduledEventRecurrenceRule and GuildScheduledEventNWeekday classes to represent and serialize recurrence data.
• Recurrence rules support weekly, monthly, and yearly patterns in accordance with Discord's official API schema.
• Includes validation logic for allowed field combinations and constraints defined by the Discord client.

Official API Docs：https://discord.com/developers/docs/resources/guild-scheduled-event#guild-scheduled-event-recurrence-rule-object

Checklist

• If code changes were made, then they have been tested
  • I have updated the documentation to reflect the changes
  • I have formatted the code properly by running pdm lint
  • I have type-checked the code by running pdm pyright
• This PR fixes an issue
• This PR adds something new (e.g. new method or parameters)
• This PR is a breaking change (e.g. methods or parameters removed/renamed)
• This PR is not a code change (e.g. documentation, README, ...)

[read-the-docs-community]

Documentation build overview

📚 disnake | 🛠️ Build #29727406 | 📁 Comparing 5626fe9 against latest (0ee7ec4)

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Show files changed (49 files in total): 📝 49 modified | ➕ 0 added | ➖ 0 deleted

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