feat: add webhook message functions

[Lacosst0]

Pull Request Type

• Feature addition
• Bugfix
• Documentation update
• Code refactor
• Tests improvement
• CI/CD pipeline enhancement
• Other: [Replace with a description]

Description

Adds Webhook.get_message() and Webhook.delete_message()
delete_message has delay parameter like Message.delete()
get_message returns None if message not found and named like http.get_webhook_message

Changes

• Added Webhook.get_message()
• Added Webhook.delete_message()

Related Issues

Test Scenarios

@slash_command()
async def test(self, ctx: SlashContext):
    webhook = await ctx.channel.create_webhook("Test")
    msg = await webhook.send("Test passed!", wait=True)

    webhook_message = await webhook.get_message(msg.id)
    print(webhook_message.content)

    await webhook.delete_message(msg.id, delay=5)
    # Test delay in delete_message
    webhook_message = await webhook.get_message(msg.id)
    print(webhook_message.content)

    await asyncio.sleep(5)
    webhook_message = await webhook.get_message(msg.id)
    if webhook_message is None:
        print("Test passed!")

Python Compatibility

• I've ensured my code works on Python 3.10.x
• I've ensured my code works on Python 3.11.x
• I've ensured my code works on Python 3.12.x

Checklist

• I've run the pre-commit code linter over all edited files
• I've tested my changes on supported Python versions
• I've added tests for my code, if applicable
• I've updated / added documentation, where applicable

Requested change happened, but unable to properly review.