Expose SCID, HTLC bounds, shutdown state, and reserve type on Channel

[elnafateh]

Part of #251.

Channel was missing several fields already available on ldk_node::ChannelDetails:

short_channel_id, outbound_scid_alias, inbound_scid_alias
inbound_htlc_minimum_msat, inbound_htlc_maximum_msat
channel_shutdown_state (new ChannelShutdownState enum)
reserve_type (new ReserveType enum) the same kind of gap

cltv_expiry_delta was also mentioned in the issue but is already exposed via channel_config, so it's left out here to avoid duplication.

Remaining items from #251 (splice events, on-chain transaction classification, misc smaller fields) left for follow-up PRs.

[ldk-reviews-bot]

I've assigned @benthecarman 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.