Reorganize the code to make it crystal clear how the same logic is implemented in Doublets and Neo4j

[konard]

Summary

This PR addresses issue #13 by reorganizing the codebase to make it crystal clear how the same logic is implemented in both Doublets and Neo4j databases.

Complete Separation of Neo4j and Doublets Code

All source files are now split into separate directories/files for easy comparison. No file contains mixed Neo4j and Doublets logic.

Benchmark Files

Directory	Purpose
rust/benches/benchmarks/neo4j/	All Neo4j benchmarks using Cypher queries
rust/benches/benchmarks/doublets/	All Doublets benchmarks using direct memory access

Library Source Files

File	Purpose
rust/src/benched/neo4j_benched.rs	Neo4j Benched trait implementations
rust/src/benched/doublets_benched.rs	Doublets Benched trait implementations
rust/src/neo4j_impl.rs	Documents how Neo4j implements the common interface
rust/src/doublets_impl.rs	Documents how Doublets implements the common interface
rust/src/client.rs	Neo4j HTTP client (pure Neo4j code)
rust/src/transaction.rs	Neo4j transaction wrapper (pure Neo4j code)

Is This Real Separation or Duplicated Code?

Yes, the benchmarks use the separate implementations!

Each benchmark file in neo4j/ or doublets/ creates and uses the appropriate storage backend:

• Neo4j benchmarks (e.g., neo4j/create.rs) instantiate Exclusive<Client<usize>> which uses HTTP API calls to Neo4j
• Doublets benchmarks (e.g., doublets/create.rs) instantiate unit::Store or split::Store which uses direct memory access

The same benchmark logic (create, update, delete, each) runs against completely different storage backends, allowing fair performance comparison.

Benchmark File Structure

Each benchmark directory has the same structure for easy side-by-side comparison:

benchmarks/neo4j/          benchmarks/doublets/
├── mod.rs                 ├── mod.rs
├── create.rs              ├── create.rs
├── update.rs              ├── update.rs
├── delete.rs              ├── delete.rs
└── each/                  └── each/
    ├── mod.rs                 ├── mod.rs
    ├── all.rs                 ├── all.rs
    ├── identity.rs            ├── identity.rs
    ├── concrete.rs            ├── concrete.rs
    ├── outgoing.rs            ├── outgoing.rs
    └── incoming.rs            └── incoming.rs

The Common Interface

Both databases implement the Doublets<T> trait from the doublets crate:

Operation	Method	Description
Create	create_point()	Insert a point link (id = source = target)
Update	update(id, src, tgt)	Modify source and target of existing link
Delete	delete(id)	Remove a link by its ID
Each All	each(handler)	Iterate all links matching [*, *, *]
Each Identity	each_by([id,*,*], h)	Find links by ID constraint
Each Concrete	each_by([*,s,t], h)	Find links by source AND target
Each Outgoing	each_by([*,s,*], h)	Find links by source (outgoing edges)
Each Incoming	each_by([*,*,t], h)	Find links by target (incoming edges)

Example: Create Operation Comparison

Neo4j (from neo4j/create.rs):

CREATE (l:Link {id: $id, source: 0, target: 0})

Doublets (from doublets/create.rs):

let id = self.allocate_next_id();
self.links[id] = Link { id, source: id, target: id };
self.source_index.insert(id, id);
self.target_index.insert(id, id);

Test Plan

• Library compiles (cargo check --lib)
• Benchmarks compile (cargo check --benches)
• CI passes

Fixes #13

🤖 Generated with Claude Code

[konard]

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[konard]

I want separate files for Neo4j and Doublets for easy to compare structure.

[konard]

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[konard]

Do we really use our new separate implementation, or we just duplicated the code?

I want clear separation between Neo4j and Doublets logic in all files, so each file that contains both logics should be split into two.

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