Expose ChannelDetails::channel_shutdown_state

[f3r10]

Summary

Closes #803.

We currently don't expose ChannelDetails::channel_shutdown_state, so there is no good way for callers to tell whether a channel is actively going through a cooperative shutdown or merely has its peer temporarily disconnected — both situations cause is_usable to become false.

This PR adds:

• A new ChannelShutdownState enum (mirroring LDK's own type) with variants NotShuttingDown, ShutdownInitiated, ResolvingHTLCs, NegotiatingClosingFee, and ShutdownComplete.
• An Option<ChannelShutdownState> field on ChannelDetails, populated from LdkChannelDetails::channel_shutdown_state via the existing From conversion.
• A typedef enum ChannelShutdownState entry in the UniFFI UDL so the field is available to Swift, Kotlin, and Python bindings.
• Public re-export of ChannelShutdownState from the crate root.

[ldk-reviews-bot]

I've assigned @tnull as a reviewer!
I'll wait for their review and will help manage the review process.
Once they submit their review, I'll check if a second reviewer would be helpful.

[Camillarhi]

Could we replace this to accurately reflect what the source from the library says Returns None for ChannelDetails serialized on LDK versions prior to 0.0.116.

[Camillarhi]

Thanks for looking into this. Could we add assertions for channel_shutdown_state in the existing integration tests? For example, after both nodes receive the channel_ready event in do_channel_full_cycle

[ldk-reviews-bot]

🔔 1st Reminder

Hey @tnull! This PR has been waiting for your review.
Please take a look when you have a chance. If you're unable to review, please let us know so we can find another reviewer.