Convert internal functional-red-black-tree fork to TypeScript

[mweidner037]

Fixes #22

[Copilot]

Pull request overview

Converts the vendored functional-red-black-tree implementation from a JS + hand-written .d.ts pair into a single TypeScript source, and updates internal persistent-map utilities to consume the new named exports—resolving downstream TS import/type errors reported in Issue #22.

Changes:

• Replace src/vendor/functional-red-black-tree.js + .d.ts with a TypeScript implementation exporting RedBlackTree (and related types).
• Update SeqMap and LeafMap to use RedBlackTree.new(...) instead of a default-export factory + Tree type.
• Add a dedicated vendored red-black-tree test suite to validate persistence and invariants.

Reviewed changes

Copilot reviewed 4 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
test/vendor/functional-red-black-tree.test.ts	Adds invariant + behavioral tests for the vendored red-black-tree subset API.
src/vendor/functional-red-black-tree.ts	New TypeScript implementation of the vendored functional red-black tree (named exports).
src/vendor/functional-red-black-tree.js	Removes the prior JS implementation in favor of the TS version.
src/vendor/functional-red-black-tree.d.ts	Removes the prior hand-maintained type declarations (now emitted from TS).
src/internal/seq_map.ts	Switches from default import + Tree type to RedBlackTree named export.
src/internal/leaf_map.ts	Switches from default import + Tree type to RedBlackTree named export.
src/id_list.ts	Minor import reordering + adds @private doc annotations for internal/test-only exports.
.prettierrc	Adds an explicit Prettier config file (empty config).

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