RGB KVStore Integration

[dcorral]

This PR adds database persistence for RGB-specific data via the KVStoreSync trait, replacing direct filesystem operations with KVStore calls while maintaining filesystem fallback for backward compatibility.

Changes

New KVStore Functions (rgb_utils/mod.rs)

Added namespace constants and persistence functions:

pub const RGB_PRIMARY_NS: &str = "rgb";
pub const RGB_CHANNEL_INFO_NS: &str = "channel_info";
pub const RGB_CHANNEL_INFO_PENDING_NS: &str = "channel_info_pending";
pub const RGB_PAYMENT_INFO_INBOUND_NS: &str = "payment_info_inbound";
pub const RGB_PAYMENT_INFO_OUTBOUND_NS: &str = "payment_info_outbound";
pub const RGB_TRANSFER_INFO_NS: &str = "transfer_info";

New functions:

• read_rgb_transfer_info_kv / write_rgb_transfer_info_kv
• read_rgb_channel_info_kv / write_rgb_channel_info_kv / remove_rgb_channel_info_kv
• read_rgb_payment_info_kv / write_rgb_payment_info_kv
• get_rgb_channel_info_pending_kv

Dependency Injection

KVStore is now passed through struct fields:

• KeysManager.rgb_kv_store
• InMemorySigner.rgb_kv_store
• OutboundPayments.rgb_kv_store
• ChannelContext.rgb_kv_store

Filesystem Fallback

All RGB functions support graceful fallback when KVStore is None:

• color_htlc - KVStore read/write with filesystem fallback
• color_closing - Uses get_rgb_channel_info_pending with fallback
• is_channel_rgb - Checks KVStore first, then filesystem
• get_rgb_channel_info - KVStore with filesystem fallback
• rename_rgb_files - Operates on both for compatibility

Design

1. Optional KVStore - All functions accept Option<&Arc<dyn KVStoreSync + Send + Sync>>
2. Backward compatible - Falls back to filesystem when KVStore unavailable

Breaking Changes

The following public functions now require an additional kv_store parameter:

Function	New Parameter
is_channel_rgb	kv_store: Option<&Arc<dyn KVStoreSync + Send + Sync>>
update_rgb_channel_amount	kv_store: Option<&Arc<dyn KVStoreSync + Send + Sync>>
write_rgb_payment_info_file	kv_store: &Arc<dyn KVStoreSync + Send + Sync> (also removed ldk_data_dir)

Callers can pass None to maintain existing filesystem-only behavior.