Update speedloader for lnd 0.20

[hsjoberg]

More graph and db refactoring happened between lnd 0.19 and 0.20 which caused speedloader to break

[gemini-code-assist]

Summary of Changes

Hello @hsjoberg, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request updates the speedloader component to maintain compatibility with the latest lnd version 0.20. It addresses significant refactoring in lnd's graph and database layers, ensuring that speedloader can correctly interact with the updated data structures and API calls. The changes primarily involve adapting to new model types, revised database initialization patterns, and the introduction of context parameters in database operations.

Highlights

• Graph Database Initialization: The initialization of the ChannelGraph has been updated to first create a graphdb.KVStore from the backend, and then use this store to instantiate the ChannelGraph.
• Model Type Update: The models.LightningNode type has been replaced with models.Node across several function signatures and variable declarations, reflecting a change in the underlying data model.
• Context Propagation: A globalCtx (context) parameter has been added to numerous graph database methods, including SourceNode, ForEachNodeChannel, SetSourceNode, AddNode, AddChannelEdge, and UpdateEdgePolicy, to support context-aware operations.
• ForEachNodeChannel Signature Change: The ForEachNodeChannel function now accepts an additional empty function argument, indicating a change in its callback mechanism or optional processing.
• Node Addition Method Renamed: The method graphKV.AddLightningNode has been renamed to graphKV.AddNode, aligning with the updated model type.
• New Import: The github.com/lightningnetwork/lnd/routing/route package has been imported, likely to support new routing-related types or functionalities, such as route.Vertex.

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[gemini-code-assist]

Code Review

This pull request updates the speedloader to be compatible with lnd 0.20. The changes primarily involve adapting to API modifications in lnd's graph and database packages. This includes using graphdb.NewKVStore, updating function signatures to pass a context, and using the models.Node type instead of the deprecated models.LightningNode. The changes are mostly correct and implement the necessary updates. I've added one comment regarding code duplication in error handling to improve maintainability.

[gemini-code-assist]

This error handling block duplicates the cleanup logic found on lines 126-127. To improve maintainability and avoid repetition, consider extracting the cleanup logic (chanDB.Close() and backend.Close()) into a local helper function or using a defer statement with a named error return to handle cleanup.