Fix critical bugs and add tests for all remaining untested JS sibling files

[loiane]

Summary

Follow-up to #283. That PR fixed bugs in the two hash-table .js files. While investigating, I found that nearly every other hand-written plain-JS "sibling" implementation (parallel to the tested TypeScript versions) also had zero test coverage — never require()'d by any test. This PR adds dedicated tests for all of them and fixes every real bug found along the way.

Result: 677 tests passing, statement coverage 94.3% → 98.65%.

Bugs fixed

src/10-tree/

• fenwick-tree.js / segment-tree.js: missing module.exports — these classes could never be require()'d at all.
• binary-search-tree.js, avl-tree.js, red-black-tree.js: internal require()s lacked explicit .js extensions, resolving to the .ts siblings instead and throwing at construction time.
• avl-tree.js & red-black-tree.js: both subclasses declared their own private #root, shadowing the base class's #root used by inherited search/min/max/traversal methods. These were silently broken — search always returned false, min/max always null, traversals were no-ops — for both classes, the whole time.
• red-black-tree.js: rotation helpers never returned the new subtree root, corrupting the tree on removal-triggered rebalancing. Also fixed a stale parent pointer left after promoting a single child during removal.

src/07-set/set.js

• has() / getSizeWithoutSizeProperty() called this.#items.hasOwnProperty() directly — throws if a value like "hasOwnProperty" was ever stored, since it shadows the prototype method.

src/08-dictionary-hash/hash-table.js

• put() used && instead of || for its null-check (allowed a null key through). remove() used a truthy check that could never remove falsy values (0, '', false). toString() crashed on an empty table and mis-formatted objects in the first bucket.

src/06-linked-list/circular-linked-list_.js

• prepend() mutated a stray public head property instead of the private #head, silently desyncing the list.
• removeAt() called a nonexistent #removeFromMiddle method — a hard crash for any middle-position removal.
• remove()/indexOf() contained leftover TypeScript type annotations, which are invalid syntax in a plain .js file and broke module parsing entirely.

queue.js, stack.js, doubly-linked-list_.js

• toString() called item.toString() on primitives, throwing on undefined items. Switched to String(item) to match the .ts siblings.

src/13-graph/*.js, src/12-trie/trie.js: no .js-specific bugs found — added full test coverage (100% stmts/branch) as a safety net.

Known pre-existing issues found but intentionally left unfixed

(identical in both .js and .ts, so out of scope for this .js-only pass)

• kruskal.js/.ts: find() uses a falsy parent-pointer check that mistreats vertex 0 as "no parent," which can leave a vertex disconnected from the MST result.
• segment-tree.js/.ts: the "no overlap" query base case always returns 0, which is only a valid identity for sum, not min/max.
• red-black-tree.js/.ts: rare duplicate-value delete sequences can produce a structurally invalid BST (fuzz-tested 300+ trials with distinct values — no failures).

Tests added

New __test__ files for every previously-untested .js module: set-js, trie-js, avl-tree-js, binary-search-tree-js, red-black-tree-js, fenwick-tree-js, segment-tree-js, graph-js, bfs-js, dfs-js, dijkstra-js, floyd-warshall-js, kruskal-js, prim-js, queue-js, stack-js, doubly-linked-list_, circular-linked-list_, hash-table-js.

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Update: the #root-shadowing bug also existed in the TypeScript files

While investigating whether these .js bugs were pre-existing "compiled output" issues, I confirmed .js and .ts are hand-written, independently-maintained parallel implementations (no build step relates them — tsconfig.json has no outDir, and some .js files here have no .ts counterpart at all).

Checking each .js fix against its .ts sibling, most were .js-only (set.ts, hash-table.ts, circular-linked-list.ts, queue.ts/stack.ts/doubly-linked-list.ts were all already correct). However, avl-tree.ts and red-black-tree.ts — the actively-tested TypeScript reference implementations — had the exact same bugs, now fixed in the latest commit:

• #root shadowing (both classes): identical to the .js bug — search() always returned false, min()/max() always null, root always null, traversals were no-ops, despite insert/remove working correctly.
• red-black-tree.ts only: #rotateLeft/#rotateRight were typed to return void and had no return statement, so #balance()'s return this.#rotateRight(node) calls (used during removal rebalancing) returned undefined, silently corrupting the tree. Also fixed a stale parent pointer left after promoting a single child during removal.

This was never caught because binary-search-tree.test.ts's AVLTree/RedBlackTree test blocks only asserted expect(() => ...).not.toThrow() — they never called search()/min()/max()/checked root, or verified traversal output. Added correctness assertions to close that gap.

Updated result: 687 tests passing, tsc --noEmit clean.