[g175] refactor: prep for multiple Node versions

[ellemouton]

A simple refactor & clean-up PR.

The main thing here is an added Version field to the models.Node struct & using a constructor to create the Node instance so that all the V1 fields are set for a V1 node. This is in preparation for dealing with V2 Nodes.

Part of #10293

[gemini-code-assist]

Summary of Changes

Hello @ellemouton, 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 is a refactor and cleanup aimed at preparing the codebase for supporting multiple versions of Lightning Network node announcements. It introduces a Version field to the models.Node struct, replaces direct struct instantiation with dedicated constructors for V1 nodes, and converts optional fields like Color and Alias to use fn.Option types. Additionally, it simplifies several related data structures by removing redundant cached fields and their accessor methods. The changes are applied consistently across the codebase, updating all relevant call sites and tests to align with the new design. This lays the groundwork for future extensions, such as V2 node announcements, while improving code clarity and maintainability.

Highlights

• Node Versioning Refactor: The core change introduces a Version field to the models.Node struct and refactors node creation to use constructors (NewV1Node, NewV1ShellNode, NewShellNode). This prepares the codebase for handling multiple node announcement versions (e.g., V1, V2).
• Optional Fields with fn.Option: The Color and Alias fields in models.Node are now wrapped in fn.Option types, making their optionality explicit. All usage sites have been updated to correctly handle these optional values using UnwrapOr or WhenSome.
• Simplified Data Structures: The HaveNodeAnnouncement boolean field in models.Node has been replaced by a HaveAnnouncement() method. Additionally, cached ecdsa.Signature fields in ChannelAuthProof and btcec.PublicKey fields in ChannelEdgeInfo have been removed, simplifying these structs and their access patterns.
• Codebase-Wide Adaption: Numerous files across the project, including tests, database implementations (kv_store, sql_store), RPC server logic, and routing components, have been updated to use the new node constructors and fn.Option access patterns, ensuring consistency with the refactored models.Node.
• Graph Interface Consolidation: The graph.DB interface has been removed, and direct usage of *graphdb.ChannelGraph is now prevalent, suggesting a consolidation of graph database access mechanisms.

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Code Review

This pull request introduces a refactor to prepare the codebase for handling multiple Node versions, specifically by adding a Version field to the models.Node struct and using a constructor to create Node instances. The changes primarily involve modifying the autopilot/prefattach_test.go, channeldb/db_test.go, discovery/chan_series.go, graph/builder.go, graph/builder_test.go, graph/db/graph.go, graph/db/graph_test.go, graph/db/interfaces.go, graph/db/kv_store.go, graph/db/models/channel_auth_proof.go, graph/db/models/channel_edge_info.go, graph/db/models/node.go, graph/db/notifications.go, graph/db/sql_migration.go, graph/db/sql_migration_test.go, lnrpc/devrpc/dev_server.go, routing/pathfind_test.go, routing/payment_session_source.go, routing/payment_session_test.go, routing/router_test.go, and server.go files. The review focuses on correctness, maintainability, and adherence to the repository's style guide, particularly concerning code documentation, commenting, spacing, and formatting.