_fallback is not copied by Parameter.replace

[LyricLy]

Summary

Using a seemingly innocuous call to replace changes the behaviour of some Parameters.

Reproduction Steps

Call the replace method on any built-in Parameter that uses the hidden _fallback field, such as Author or CurrentChannel.

Minimal Reproducible Code

# only accepts text channels, as expected
@commands.command()
async def foo(ctx, channel: TextChannel = commands.CurrentChannel):
    await ctx.send(x.name)

# accepts any kind of channel, ignoring the annotation
@commands.command()
async def bar(ctx, channel: TextChannel = commands.CurrentChannel.replace(description="A text channel to use.")):
    await ctx.send(x.name)

Expected Results

I expect .replace(description=...), which looks like it should only change the description of the parameter, not to change the behaviour of how it parses.

Actual Results

As the replace method does not copy _fallback, the special behaviour of CurrentChannel to prioritize the annotation in picking a converter is lost.

Intents

guilds, messages, message_content.

System Information

- Python v3.13.1-final
- discord.py v2.4.0-final
- aiohttp v3.10.5
- system info: Linux 6.12.9-arch1-1 #1 SMP PREEMPT_DYNAMIC Fri, 10 Jan 2025 00:39:41 +0000

Checklist

• I have searched the open issues for duplicates.
• I have shown the entire traceback, if possible.
• I have removed my token from display, if visible.

Additional Context

No response