feat: bfs dijkstra flow map

[Malibu-With-Coke]

What

Add a dedicated BFS flow map, update Dijkstra maps to use a priority queue for weighted shortest-path costs, and add BFS example/docs coverage.

Why

The previous DijkstraMap implementation used FIFO queue traversal, which behaves more like BFS/flood fill and can produce incorrect results with non-uniform exit costs. Splitting BFS into BfsMap and moving DijkstraMap to BinaryHeap keeps the algorithm roles clear and makes weighted path costs correct.

Closes #32

Checklist

Required

• cargo check --all passes
• cargo fmt --all -- --check passes
• cargo clippy --workspace --all-targets -- -D warnings -A clippy::multiple-crate-versions passes
• cargo test --all passes
• I linked the related issue (for example: Closes #123)

Functional Validation

• Behavior related to this change was verified locally (if applicable)
• Rendering/backend behavior was verified when runtime code changed (if applicable)
• Algorithm behavior (pathfinding/FOV/noise/random) was verified when affected (if applicable)
• I added or updated tests for changed behavior (if applicable)

Configuration & Docs

• User-facing docs were updated (README.md, ARCHITECTURE.md, or relevant manual pages, if applicable)
• New dependencies/configuration are documented (if applicable)
• No sensitive values or credentials were introduced

If Applicable

• Security impact considered (run cargo audit locally if needed)
• Breaking behavior changes are clearly described in this PR

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